From 83b3d6934620544eb44849e67e4488e1a56a7f30 Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Mon, 27 Apr 2026 15:49:03 +0200
Subject: [PATCH 01/19] Fix missing PEFT availability check for peft_config in
 exp trainers

---
 trl/experimental/distillation/distillation_trainer.py | 5 +++++
 trl/experimental/tpo/tpo_trainer.py                   | 6 ++++++
 2 files changed, 11 insertions(+)

diff --git a/trl/experimental/distillation/distillation_trainer.py b/trl/experimental/distillation/distillation_trainer.py
index 77dbcc6c08e..ebd7ce1e1b1 100644
--- a/trl/experimental/distillation/distillation_trainer.py
+++ b/trl/experimental/distillation/distillation_trainer.py
@@ -429,6 +429,11 @@ def __init__(
                 processing_class.pad_token = processing_class.eos_token
 
         # ── PEFT ──
+        if peft_config is not None and not is_peft_available():
+            raise ImportError(
+                "You passed `peft_config` but the `peft` library is not installed. "
+                "Install it with `pip install trl[peft]`."
+            )
         if peft_config is not None:
             model = get_peft_model(model, peft_config)
 
diff --git a/trl/experimental/tpo/tpo_trainer.py b/trl/experimental/tpo/tpo_trainer.py
index 544c0674cca..57478a6281d 100644
--- a/trl/experimental/tpo/tpo_trainer.py
+++ b/trl/experimental/tpo/tpo_trainer.py
@@ -350,6 +350,12 @@ def __init__(
         if tokenizer.pad_token is None:
             tokenizer.pad_token = tokenizer.eos_token
 
+        # PEFT
+        if peft_config is not None and not is_peft_available():
+            raise ImportError(
+                "You passed `peft_config` but the `peft` library is not installed. "
+                "Install it with `pip install trl[peft]`."
+            )
         if is_peft_available() and is_peft_model(model) and peft_config is not None:
             raise ValueError(
                 "You passed a `PeftModel` instance together with a `peft_config` to the trainer. Please first merge "

From 32e87641e9988c793d22f7ad202fb4e9441643a0 Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Mon, 27 Apr 2026 16:27:31 +0200
Subject: [PATCH 02/19] Fix missing PEFT availability check in BCO

---
 trl/experimental/bco/bco_trainer.py | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/trl/experimental/bco/bco_trainer.py b/trl/experimental/bco/bco_trainer.py
index 9cdf47c65ee..099d3b5436f 100644
--- a/trl/experimental/bco/bco_trainer.py
+++ b/trl/experimental/bco/bco_trainer.py
@@ -469,13 +469,14 @@ def __init__(
         if isinstance(ref_model, str):
             ref_model = AutoModelForCausalLM.from_pretrained(ref_model, **model_init_kwargs)
 
+        # PEFT
         # Initialize this variable to False. This helps tracking the case when `peft_module_casting_to_bf16`
         # has been called in order to properly call autocast if needed.
         self._peft_has_been_casted_to_bf16 = False
-
-        if not is_peft_available() and peft_config is not None:
-            raise ValueError(
-                "PEFT is not installed and you passed a `peft_config` in the trainer's kwargs, please install it with `pip install peft` to use the PEFT models"
+        if peft_config is not None and not is_peft_available():
+            raise ImportError(
+                "You passed `peft_config` but the `peft` library is not installed. "
+                "Install it with `pip install trl[peft]`."
             )
         elif is_peft_available() and peft_config is not None:
             if isinstance(model, PeftModel):

From 34a141b8772691f705d74d80dbd4f208a8e5cdb8 Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Mon, 27 Apr 2026 16:27:44 +0200
Subject: [PATCH 03/19] Fix missing PEFT availability check in CPO

---
 trl/experimental/cpo/cpo_trainer.py | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/trl/experimental/cpo/cpo_trainer.py b/trl/experimental/cpo/cpo_trainer.py
index f3e0f39920e..c403951eb7a 100644
--- a/trl/experimental/cpo/cpo_trainer.py
+++ b/trl/experimental/cpo/cpo_trainer.py
@@ -169,13 +169,14 @@ def __init__(
         if isinstance(model, str):
             model = AutoModelForCausalLM.from_pretrained(model, **model_init_kwargs)
 
+        # PEFT
         # Initialize this variable to False. This helps tracking the case when `peft_module_casting_to_bf16`
         # has been called in order to properly call autocast if needed.
         self._peft_has_been_casted_to_bf16 = False
-
-        if not is_peft_available() and peft_config is not None:
-            raise ValueError(
-                "PEFT is not installed and you passed a `peft_config` in the trainer's kwargs, please install it to use the PEFT models"
+        if peft_config is not None and not is_peft_available():
+            raise ImportError(
+                "You passed `peft_config` but the `peft` library is not installed. "
+                "Install it with `pip install trl[peft]`."
             )
         elif is_peft_available() and peft_config is not None:
             if isinstance(model, PeftModel):

From 8eb11c56ad7246e3eb9b440487c62ee9856f019e Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Mon, 27 Apr 2026 16:28:15 +0200
Subject: [PATCH 04/19] Fix missing PEFT availability check in KTO

---
 trl/experimental/kto/kto_trainer.py | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/trl/experimental/kto/kto_trainer.py b/trl/experimental/kto/kto_trainer.py
index 14359f8bd70..f6d989923f1 100644
--- a/trl/experimental/kto/kto_trainer.py
+++ b/trl/experimental/kto/kto_trainer.py
@@ -289,13 +289,14 @@ def __init__(
         if tokenizer.pad_token is None:
             tokenizer.pad_token = tokenizer.eos_token
 
+        # PEFT
         # Initialize this variable to False. This helps tracking the case when `peft_module_casting_to_bf16`
         # has been called in order to properly call autocast if needed.
         self._peft_has_been_casted_to_bf16 = False
-
-        if not is_peft_available() and peft_config is not None:
-            raise ValueError(
-                "PEFT is not installed and you passed a `peft_config` in the trainer's kwargs, please install it with `pip install peft` to use the PEFT models"
+        if peft_config is not None and not is_peft_available():
+            raise ImportError(
+                "You passed `peft_config` but the `peft` library is not installed. "
+                "Install it with `pip install trl[peft]`."
             )
         if is_peft_available() and isinstance(model, PeftModel) and peft_config is not None:
             raise ValueError(

From 0d6660d94e787dcb434a3db5890bfa3df2bf5bb9 Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Mon, 27 Apr 2026 16:28:28 +0200
Subject: [PATCH 05/19] Fix missing PEFT availability check in ORPO

---
 trl/experimental/orpo/orpo_trainer.py | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/trl/experimental/orpo/orpo_trainer.py b/trl/experimental/orpo/orpo_trainer.py
index 59d7636efb7..04a870dfb2d 100644
--- a/trl/experimental/orpo/orpo_trainer.py
+++ b/trl/experimental/orpo/orpo_trainer.py
@@ -178,13 +178,14 @@ def __init__(
         if isinstance(model, str):
             model = AutoModelForCausalLM.from_pretrained(model, **model_init_kwargs)
 
+        # PEFT
         # Initialize this variable to False. This helps tracking the case when `peft_module_casting_to_bf16`
         # has been called in order to properly call autocast if needed.
         self._peft_has_been_casted_to_bf16 = False
-
-        if not is_peft_available() and peft_config is not None:
-            raise ValueError(
-                "PEFT is not installed and you passed a `peft_config` in the trainer's kwargs, please install it to use the PEFT models"
+        if peft_config is not None and not is_peft_available():
+            raise ImportError(
+                "You passed `peft_config` but the `peft` library is not installed. "
+                "Install it with `pip install trl[peft]`."
             )
         elif is_peft_available() and peft_config is not None:
             if isinstance(model, PeftModel):

From 3a62cf986c3c2a666fb93b7133eff806f4ec56a3 Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Mon, 27 Apr 2026 16:28:37 +0200
Subject: [PATCH 06/19] Fix missing PEFT availability check in PPO

---
 trl/experimental/ppo/ppo_trainer.py | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/trl/experimental/ppo/ppo_trainer.py b/trl/experimental/ppo/ppo_trainer.py
index 6366f987ec4..1432a06861f 100644
--- a/trl/experimental/ppo/ppo_trainer.py
+++ b/trl/experimental/ppo/ppo_trainer.py
@@ -416,10 +416,11 @@ def __init__(
                 "[Approximating KL Divergence](http://joschu.net/blog/kl-approx.html) for details."
             )
 
-        # peft support
-        if not is_peft_available() and peft_config is not None:
+        # PEFT
+        if peft_config is not None and not is_peft_available():
             raise ImportError(
-                "PEFT is not installed and you passed a `peft_config` in the trainer's kwargs, please install it to use the PEFT models"
+                "You passed `peft_config` but the `peft` library is not installed. "
+                "Install it with `pip install trl[peft]`."
             )
         elif is_peft_available() and peft_config is not None:
             if isinstance(self.policy_model, PeftModel):

From 3f3be7b94fcb65bd715223895261b8601bc7b24d Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Mon, 27 Apr 2026 19:01:57 +0200
Subject: [PATCH 07/19] Add TypeError check to Distillation

---
 .../distillation/distillation_trainer.py         | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/trl/experimental/distillation/distillation_trainer.py b/trl/experimental/distillation/distillation_trainer.py
index ebd7ce1e1b1..02bb625cd1f 100644
--- a/trl/experimental/distillation/distillation_trainer.py
+++ b/trl/experimental/distillation/distillation_trainer.py
@@ -429,11 +429,17 @@ def __init__(
                 processing_class.pad_token = processing_class.eos_token
 
         # ── PEFT ──
-        if peft_config is not None and not is_peft_available():
-            raise ImportError(
-                "You passed `peft_config` but the `peft` library is not installed. "
-                "Install it with `pip install trl[peft]`."
-            )
+        if peft_config is not None:
+            if not is_peft_available():
+                raise ImportError(
+                    "You passed `peft_config` but the `peft` library is not installed. "
+                    "Install it with `pip install trl[peft]`."
+                )
+            if not isinstance(peft_config, PeftConfig):
+                raise TypeError(
+                    f"`peft_config` must be a `peft.PeftConfig` instance (e.g. `peft.LoraConfig`), "
+                    f"got {type(peft_config).__name__}."
+                )
         if peft_config is not None:
             model = get_peft_model(model, peft_config)
 

From f5711555025ff6aa155a2cb9bceefa7cce07226a Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Mon, 27 Apr 2026 19:02:17 +0200
Subject: [PATCH 08/19] Add TypeError check to PPO

---
 trl/experimental/ppo/ppo_trainer.py | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/trl/experimental/ppo/ppo_trainer.py b/trl/experimental/ppo/ppo_trainer.py
index 1432a06861f..0d3e32f0a46 100644
--- a/trl/experimental/ppo/ppo_trainer.py
+++ b/trl/experimental/ppo/ppo_trainer.py
@@ -417,12 +417,17 @@ def __init__(
             )
 
         # PEFT
-        if peft_config is not None and not is_peft_available():
-            raise ImportError(
-                "You passed `peft_config` but the `peft` library is not installed. "
-                "Install it with `pip install trl[peft]`."
-            )
-        elif is_peft_available() and peft_config is not None:
+        if peft_config is not None:
+            if not is_peft_available():
+                raise ImportError(
+                    "You passed `peft_config` but the `peft` library is not installed. "
+                    "Install it with `pip install trl[peft]`."
+                )
+            if not isinstance(peft_config, PeftConfig):
+                raise TypeError(
+                    f"`peft_config` must be a `peft.PeftConfig` instance (e.g. `peft.LoraConfig`), "
+                    f"got {type(peft_config).__name__}."
+                )
             if isinstance(self.policy_model, PeftModel):
                 raise ValueError(
                     "You passed a `PeftModel` instance together with a `peft_config` to the trainer. Please first "

From d2664dc2285ce069575e5b9420085693ea5a89bc Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Mon, 27 Apr 2026 19:02:31 +0200
Subject: [PATCH 09/19] Add TypeError check to TPO

---
 trl/experimental/tpo/tpo_trainer.py | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/trl/experimental/tpo/tpo_trainer.py b/trl/experimental/tpo/tpo_trainer.py
index 57478a6281d..7195596e15c 100644
--- a/trl/experimental/tpo/tpo_trainer.py
+++ b/trl/experimental/tpo/tpo_trainer.py
@@ -351,11 +351,17 @@ def __init__(
             tokenizer.pad_token = tokenizer.eos_token
 
         # PEFT
-        if peft_config is not None and not is_peft_available():
-            raise ImportError(
-                "You passed `peft_config` but the `peft` library is not installed. "
-                "Install it with `pip install trl[peft]`."
-            )
+        if peft_config is not None:
+            if not is_peft_available():
+                raise ImportError(
+                    "You passed `peft_config` but the `peft` library is not installed. "
+                    "Install it with `pip install trl[peft]`."
+                )
+            if not isinstance(peft_config, PeftConfig):
+                raise TypeError(
+                    f"`peft_config` must be a `peft.PeftConfig` instance (e.g. `peft.LoraConfig`), "
+                    f"got {type(peft_config).__name__}."
+                )
         if is_peft_available() and is_peft_model(model) and peft_config is not None:
             raise ValueError(
                 "You passed a `PeftModel` instance together with a `peft_config` to the trainer. Please first merge "

From e7242f34a91abe44d77665440055021ee8570791 Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Mon, 27 Apr 2026 19:06:23 +0200
Subject: [PATCH 10/19] Add TypeError check to BCO

---
 trl/experimental/bco/bco_trainer.py | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/trl/experimental/bco/bco_trainer.py b/trl/experimental/bco/bco_trainer.py
index 099d3b5436f..a5a10725ae0 100644
--- a/trl/experimental/bco/bco_trainer.py
+++ b/trl/experimental/bco/bco_trainer.py
@@ -65,7 +65,7 @@
 
 
 if is_peft_available():
-    from peft import PeftModel, get_peft_model, prepare_model_for_kbit_training
+    from peft import PeftConfig, PeftModel, get_peft_model, prepare_model_for_kbit_training
 
 if is_wandb_available():
     import wandb
@@ -473,12 +473,17 @@ def __init__(
         # Initialize this variable to False. This helps tracking the case when `peft_module_casting_to_bf16`
         # has been called in order to properly call autocast if needed.
         self._peft_has_been_casted_to_bf16 = False
-        if peft_config is not None and not is_peft_available():
-            raise ImportError(
-                "You passed `peft_config` but the `peft` library is not installed. "
-                "Install it with `pip install trl[peft]`."
-            )
-        elif is_peft_available() and peft_config is not None:
+        if peft_config is not None:
+            if not is_peft_available():
+                raise ImportError(
+                    "You passed `peft_config` but the `peft` library is not installed. "
+                    "Install it with `pip install trl[peft]`."
+                )
+            if not isinstance(peft_config, PeftConfig):
+                raise TypeError(
+                    f"`peft_config` must be a `peft.PeftConfig` instance (e.g. `peft.LoraConfig`), "
+                    f"got {type(peft_config).__name__}."
+                )
             if isinstance(model, PeftModel):
                 raise ValueError(
                     "You passed a `PeftModel` instance together with a `peft_config` to the trainer. Please first "

From 1392892a76254ffd0061c28052fa1735d7e559a5 Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Mon, 27 Apr 2026 19:06:43 +0200
Subject: [PATCH 11/19] Add TypeError check to CPO

---
 trl/experimental/cpo/cpo_trainer.py | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/trl/experimental/cpo/cpo_trainer.py b/trl/experimental/cpo/cpo_trainer.py
index c403951eb7a..432c0bfd070 100644
--- a/trl/experimental/cpo/cpo_trainer.py
+++ b/trl/experimental/cpo/cpo_trainer.py
@@ -61,7 +61,7 @@
 
 
 if is_peft_available():
-    from peft import PeftModel, get_peft_model, prepare_model_for_kbit_training
+    from peft import PeftConfig, PeftModel, get_peft_model, prepare_model_for_kbit_training
 
 
 if is_wandb_available():
@@ -173,12 +173,17 @@ def __init__(
         # Initialize this variable to False. This helps tracking the case when `peft_module_casting_to_bf16`
         # has been called in order to properly call autocast if needed.
         self._peft_has_been_casted_to_bf16 = False
-        if peft_config is not None and not is_peft_available():
-            raise ImportError(
-                "You passed `peft_config` but the `peft` library is not installed. "
-                "Install it with `pip install trl[peft]`."
-            )
-        elif is_peft_available() and peft_config is not None:
+        if peft_config is not None:
+            if not is_peft_available():
+                raise ImportError(
+                    "You passed `peft_config` but the `peft` library is not installed. "
+                    "Install it with `pip install trl[peft]`."
+                )
+            if not isinstance(peft_config, PeftConfig):
+                raise TypeError(
+                    f"`peft_config` must be a `peft.PeftConfig` instance (e.g. `peft.LoraConfig`), "
+                    f"got {type(peft_config).__name__}."
+                )
             if isinstance(model, PeftModel):
                 raise ValueError(
                     "You passed a `PeftModel` instance together with a `peft_config` to the trainer. Please first "

From 811f87f3ac159382e5866f9664010b2315c3c51e Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Mon, 27 Apr 2026 19:07:07 +0200
Subject: [PATCH 12/19] Add TypeError check to KTO

---
 trl/experimental/kto/kto_trainer.py | 30 +++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/trl/experimental/kto/kto_trainer.py b/trl/experimental/kto/kto_trainer.py
index f6d989923f1..757fbad8a68 100644
--- a/trl/experimental/kto/kto_trainer.py
+++ b/trl/experimental/kto/kto_trainer.py
@@ -67,7 +67,7 @@
     from liger_kernel.chunked_loss import LigerFusedLinearKTOLoss
 
 if is_peft_available():
-    from peft import PeftModel, get_peft_model, prepare_model_for_kbit_training
+    from peft import PeftConfig, PeftModel, get_peft_model, prepare_model_for_kbit_training
 
 
 if TYPE_CHECKING:
@@ -293,17 +293,23 @@ def __init__(
         # Initialize this variable to False. This helps tracking the case when `peft_module_casting_to_bf16`
         # has been called in order to properly call autocast if needed.
         self._peft_has_been_casted_to_bf16 = False
-        if peft_config is not None and not is_peft_available():
-            raise ImportError(
-                "You passed `peft_config` but the `peft` library is not installed. "
-                "Install it with `pip install trl[peft]`."
-            )
-        if is_peft_available() and isinstance(model, PeftModel) and peft_config is not None:
-            raise ValueError(
-                "You passed a `PeftModel` instance together with a `peft_config` to the trainer. Please first merge "
-                "and unload the existing adapter, save the resulting base model, and then pass that base model along "
-                "with the new `peft_config` to the trainer."
-            )
+        if peft_config is not None:
+            if not is_peft_available():
+                raise ImportError(
+                    "You passed `peft_config` but the `peft` library is not installed. "
+                    "Install it with `pip install trl[peft]`."
+                )
+            if not isinstance(peft_config, PeftConfig):
+                raise TypeError(
+                    f"`peft_config` must be a `peft.PeftConfig` instance (e.g. `peft.LoraConfig`), "
+                    f"got {type(peft_config).__name__}."
+                )
+            if isinstance(model, PeftModel):
+                raise ValueError(
+                    "You passed a `PeftModel` instance together with a `peft_config` to the trainer. Please first merge "
+                    "and unload the existing adapter, save the resulting base model, and then pass that base model along "
+                    "with the new `peft_config` to the trainer."
+                )
         if is_peft_available() and isinstance(model, PeftModel) and ref_model is None:
             # If the model is a PEFT model with a pretrained adapter, we need to create a "ref" adapter that is a copy
             # of the "default" adapter, so that we can use it as the reference model during KTO training.

From 3d487c81f396f8d97974e1bb591bf920213d9875 Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Mon, 27 Apr 2026 19:07:30 +0200
Subject: [PATCH 13/19] Add TypeError check to ORPO

---
 trl/experimental/orpo/orpo_trainer.py | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/trl/experimental/orpo/orpo_trainer.py b/trl/experimental/orpo/orpo_trainer.py
index 04a870dfb2d..22e6a81fbf6 100644
--- a/trl/experimental/orpo/orpo_trainer.py
+++ b/trl/experimental/orpo/orpo_trainer.py
@@ -62,7 +62,7 @@
 
 
 if is_peft_available():
-    from peft import PeftModel, get_peft_model, prepare_model_for_kbit_training
+    from peft import PeftConfig, PeftModel, get_peft_model, prepare_model_for_kbit_training
 
 
 if is_wandb_available():
@@ -182,12 +182,17 @@ def __init__(
         # Initialize this variable to False. This helps tracking the case when `peft_module_casting_to_bf16`
         # has been called in order to properly call autocast if needed.
         self._peft_has_been_casted_to_bf16 = False
-        if peft_config is not None and not is_peft_available():
-            raise ImportError(
-                "You passed `peft_config` but the `peft` library is not installed. "
-                "Install it with `pip install trl[peft]`."
-            )
-        elif is_peft_available() and peft_config is not None:
+        if peft_config is not None:
+            if not is_peft_available():
+                raise ImportError(
+                    "You passed `peft_config` but the `peft` library is not installed. "
+                    "Install it with `pip install trl[peft]`."
+                )
+            if not isinstance(peft_config, PeftConfig):
+                raise TypeError(
+                    f"`peft_config` must be a `peft.PeftConfig` instance (e.g. `peft.LoraConfig`), "
+                    f"got {type(peft_config).__name__}."
+                )
             if isinstance(model, PeftModel):
                 raise ValueError(
                     "You passed a `PeftModel` instance together with a `peft_config` to the trainer. Please first "

From ef4149df75ad7b9d67eb2ea13e148c12453da250 Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Mon, 27 Apr 2026 20:08:58 +0200
Subject: [PATCH 14/19] Add PEFT validation to PRM

---
 trl/experimental/prm/prm_trainer.py | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/trl/experimental/prm/prm_trainer.py b/trl/experimental/prm/prm_trainer.py
index 7b26b69bd82..c6bf17ad453 100644
--- a/trl/experimental/prm/prm_trainer.py
+++ b/trl/experimental/prm/prm_trainer.py
@@ -44,7 +44,7 @@
 
 
 if is_peft_available():
-    from peft import PeftModel
+    from peft import PeftConfig, PeftModel
 
 logger = logging.get_logger(__name__)
 
@@ -172,6 +172,18 @@ def __init__(
         if train_dataset is None:
             raise ValueError("`train_dataset` is required")
 
+        # PEFT
+        if peft_config is not None:
+            if not is_peft_available():
+                raise ImportError(
+                    "You passed `peft_config` but the `peft` library is not installed. "
+                    "Install it with `pip install trl[peft]`."
+                )
+            if not isinstance(peft_config, PeftConfig):
+                raise TypeError(
+                    f"`peft_config` must be a `peft.PeftConfig` instance (e.g. `peft.LoraConfig`), "
+                    f"got {type(peft_config).__name__}."
+                )
         if peft_config is not None or (is_peft_available() and isinstance(model, PeftModel)):
             model = prepare_peft_model(model, peft_config, args)
 

From 7179659c5019ec6a3b4d5beba260f87bcc7d33c3 Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Mon, 27 Apr 2026 20:09:22 +0200
Subject: [PATCH 15/19] Add PEFT validation to OnlineDPO

---
 trl/experimental/online_dpo/online_dpo_trainer.py | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/trl/experimental/online_dpo/online_dpo_trainer.py b/trl/experimental/online_dpo/online_dpo_trainer.py
index 4c7adef3b6d..5cb73fbcc83 100644
--- a/trl/experimental/online_dpo/online_dpo_trainer.py
+++ b/trl/experimental/online_dpo/online_dpo_trainer.py
@@ -282,6 +282,18 @@ def __init__(
         self.is_encoder_decoder = model.config.is_encoder_decoder
         self.is_vision_model = model.config.model_type in MODEL_FOR_IMAGE_TEXT_TO_TEXT_MAPPING_NAMES.keys()
 
+        # PEFT
+        if peft_config is not None:
+            if not is_peft_available():
+                raise ImportError(
+                    "You passed `peft_config` but the `peft` library is not installed. "
+                    "Install it with `pip install trl[peft]`."
+                )
+            if not isinstance(peft_config, PeftConfig):
+                raise TypeError(
+                    f"`peft_config` must be a `peft.PeftConfig` instance (e.g. `peft.LoraConfig`), "
+                    f"got {type(peft_config).__name__}."
+                )
         if peft_config is not None or (is_peft_available() and isinstance(model, PeftModel)):
             model = prepare_peft_model(model, peft_config, args)
 

From d0a75622e52e8736230351d59938413ed6a3f54e Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Mon, 27 Apr 2026 20:27:03 +0200
Subject: [PATCH 16/19] Remove redundant duplicate condition check in
 Distillation

---
 trl/experimental/distillation/distillation_trainer.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/trl/experimental/distillation/distillation_trainer.py b/trl/experimental/distillation/distillation_trainer.py
index 02bb625cd1f..f80dd19358a 100644
--- a/trl/experimental/distillation/distillation_trainer.py
+++ b/trl/experimental/distillation/distillation_trainer.py
@@ -440,7 +440,6 @@ def __init__(
                     f"`peft_config` must be a `peft.PeftConfig` instance (e.g. `peft.LoraConfig`), "
                     f"got {type(peft_config).__name__}."
                 )
-        if peft_config is not None:
             model = get_peft_model(model, peft_config)
 
         # ── Data collator ──

From 9f2cd225e2ac89dfa434726e4b495e55a646a839 Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Tue, 28 Apr 2026 08:08:58 +0200
Subject: [PATCH 17/19] Add PEFT validation to SDFT

---
 trl/experimental/sdft/sdft_trainer.py | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/trl/experimental/sdft/sdft_trainer.py b/trl/experimental/sdft/sdft_trainer.py
index 5bf6095c2a0..a4be9b395fe 100644
--- a/trl/experimental/sdft/sdft_trainer.py
+++ b/trl/experimental/sdft/sdft_trainer.py
@@ -195,6 +195,18 @@ def __init__(
             else inspect.signature(model.get_base_model().forward).parameters.keys()
         )
 
+        # PEFT
+        if peft_config is not None:
+            if not is_peft_available():
+                raise ImportError(
+                    "You passed `peft_config` but the `peft` library is not installed. "
+                    "Install it with `pip install trl[peft]`."
+                )
+            if not isinstance(peft_config, PeftConfig):
+                raise TypeError(
+                    f"`peft_config` must be a `peft.PeftConfig` instance (e.g. `peft.LoraConfig`), "
+                    f"got {type(peft_config).__name__}."
+                )
         if is_peft_available() and is_peft_model(model) and peft_config is not None:
             raise ValueError(
                 "You passed a `PeftModel` instance together with a `peft_config` to SDFTTrainer. Pass either a base "

From 81cb6f213d771af17b06b32462c89dc2d70b6647 Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Tue, 28 Apr 2026 08:09:10 +0200
Subject: [PATCH 18/19] Add PEFT validation to BaseSelfDistillation

---
 .../base_self_distillation_trainer.py                | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/trl/experimental/self_distillation/base_self_distillation_trainer.py b/trl/experimental/self_distillation/base_self_distillation_trainer.py
index bd9abb95164..5484a2efb66 100644
--- a/trl/experimental/self_distillation/base_self_distillation_trainer.py
+++ b/trl/experimental/self_distillation/base_self_distillation_trainer.py
@@ -104,6 +104,18 @@ def __init__(
             else inspect.signature(model.get_base_model().forward).parameters.keys()
         )
 
+        # PEFT
+        if peft_config is not None:
+            if not is_peft_available():
+                raise ImportError(
+                    "You passed `peft_config` but the `peft` library is not installed. "
+                    "Install it with `pip install trl[peft]`."
+                )
+            if not isinstance(peft_config, PeftConfig):
+                raise TypeError(
+                    f"`peft_config` must be a `peft.PeftConfig` instance (e.g. `peft.LoraConfig`), "
+                    f"got {type(peft_config).__name__}."
+                )
         if peft_config is not None or (is_peft_available() and getattr(model, "peft_config", None) is not None):
             model = prepare_peft_model(model, peft_config, args)
 

From 81153c80548c9860004f41599a905262de08ef38 Mon Sep 17 00:00:00 2001
From: Albert Villanova del Moral
 <8515462+albertvillanova@users.noreply.github.com>
Date: Tue, 28 Apr 2026 08:09:23 +0200
Subject: [PATCH 19/19] Add PEFT validation to SSD

---
 trl/experimental/ssd/ssd_trainer.py | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/trl/experimental/ssd/ssd_trainer.py b/trl/experimental/ssd/ssd_trainer.py
index ea378753653..91a0275047a 100644
--- a/trl/experimental/ssd/ssd_trainer.py
+++ b/trl/experimental/ssd/ssd_trainer.py
@@ -135,6 +135,18 @@ def __init__(
             else inspect.signature(model.get_base_model().forward).parameters.keys()
         )
 
+        # PEFT
+        if peft_config is not None:
+            if not is_peft_available():
+                raise ImportError(
+                    "You passed `peft_config` but the `peft` library is not installed. "
+                    "Install it with `pip install trl[peft]`."
+                )
+            if not isinstance(peft_config, PeftConfig):
+                raise TypeError(
+                    f"`peft_config` must be a `peft.PeftConfig` instance (e.g. `peft.LoraConfig`), "
+                    f"got {type(peft_config).__name__}."
+                )
         if is_peft_available() and is_peft_model(model) and peft_config is not None:
             raise ValueError(
                 "You passed a `PeftModel` instance together with a `peft_config` to SSDTrainer. Pass either a base "