diff --git a/.changeset/neon-ai-gateway-models.md b/.changeset/neon-ai-gateway-models.md
new file mode 100644
index 0000000..471a7d8
--- /dev/null
+++ b/.changeset/neon-ai-gateway-models.md
@@ -0,0 +1,12 @@
+---
+"@upstash/box": patch
+"@upstash/box-cli": patch
+---
+
+Add Neon AI Gateway models: `NeonModel` (`neon/<neon-short-id>`) for the Codex and
+OpenCode harnesses. `inferDefaultProvider` routes `neon/gpt-*` to Codex, except
+`neon/gpt-oss-*`, and every other Neon model to OpenCode (GPT OSS, Claude, Gemini,
+Llama, Qwen, Kimi, GLM, Grok). Neon's Claude models run on OpenCode only, because Neon
+serves them through chat completions and not the Responses API. Box does not run
+Claude Code with Neon. The CLI model picker lists them for Codex and OpenCode.
+Runs use the Neon credential (token and branch base URL) saved in the console.
diff --git a/packages/cli/src/__tests__/commands/create-wizard.test.ts b/packages/cli/src/__tests__/commands/create-wizard.test.ts
index f75e523..25add61 100644
--- a/packages/cli/src/__tests__/commands/create-wizard.test.ts
+++ b/packages/cli/src/__tests__/commands/create-wizard.test.ts
@@ -82,6 +82,26 @@ describe("createWizard", () => {
     });
   });
 
+  it("Neon model → stored credential without asking for a key", async () => {
+    vi.mocked(interactiveSelect)
+      .mockResolvedValueOnce("node") // runtime
+      .mockResolvedValueOnce("agent") // action: configure agent
+      .mockResolvedValueOnce("opencode") // provider
+      .mockResolvedValueOnce("neon/claude-haiku-4-5") // model
+      .mockResolvedValueOnce("create"); // action: create (no key prompt in between)
+
+    const result = await createWizard();
+
+    expect(result).toEqual({
+      runtime: "node",
+      agentModel: "neon/claude-haiku-4-5",
+      agentProvider: "opencode",
+      agentApiKey: "stored",
+    });
+    // runtime, action, provider, model, action: the key choice was never shown.
+    expect(vi.mocked(interactiveSelect)).toHaveBeenCalledTimes(5);
+  });
+
   it("stored key option → agentApiKey is 'stored'", async () => {
     vi.mocked(interactiveSelect)
       .mockResolvedValueOnce("node") // runtime
diff --git a/packages/cli/src/__tests__/models.test.ts b/packages/cli/src/__tests__/models.test.ts
index 9d8453d..61767f4 100644
--- a/packages/cli/src/__tests__/models.test.ts
+++ b/packages/cli/src/__tests__/models.test.ts
@@ -3,6 +3,7 @@ import {
   Agent,
   ClaudeCode,
   CursorModel,
+  NeonModel,
   OpenAICodex,
   OpenCodeModel,
   OpenRouterModel,
@@ -88,6 +89,44 @@ describe("MODEL_OPTIONS_BY_AGENT", () => {
     expect(group?.options).toContainEqual({ value, label });
   });
 
+  it("offers Neon AI Gateway models only to Codex and OpenCode", () => {
+    const groupFor = (agent: Agent) =>
+      MODEL_OPTIONS_BY_AGENT[agent].find(({ label }) => label === "Neon AI Gateway");
+
+    expect(groupFor(Agent.ClaudeCode)).toBeUndefined();
+    expect(groupFor(Agent.Cursor)).toBeUndefined();
+    expect(groupFor(Agent.Codex)?.options).toContainEqual({
+      value: NeonModel.GPT_5_5,
+      label: "GPT-5.5 (Neon)",
+    });
+    expect(groupFor(Agent.OpenCode)?.options).toContainEqual({
+      value: NeonModel.Gemini_3_6_Flash,
+      label: "Gemini 3.6 Flash (Neon)",
+    });
+  });
+
+  it("splits Neon models by endpoint support", () => {
+    const values = (agent: Agent) =>
+      MODEL_OPTIONS_BY_AGENT[agent]
+        .find(({ label }) => label === "Neon AI Gateway")
+        ?.options.map((o) => o.value) ?? [];
+
+    // Responses-only on Neon: Codex yes, OpenCode no.
+    expect(values(Agent.Codex)).toContain(NeonModel.GPT_5_5_Pro);
+    expect(values(Agent.Codex)).toContain(NeonModel.GPT_5_3_Codex);
+    expect(values(Agent.OpenCode)).not.toContain(NeonModel.GPT_5_5_Pro);
+    expect(values(Agent.OpenCode)).not.toContain(NeonModel.GPT_5_3_Codex);
+    // Chat-only on Neon: OpenCode yes, Codex no.
+    expect(values(Agent.OpenCode)).toContain(NeonModel.GPT_OSS_120B);
+    expect(values(Agent.OpenCode)).toContain(NeonModel.Kimi_K3);
+    expect(values(Agent.Codex)).not.toContain(NeonModel.GPT_OSS_120B);
+    expect(values(Agent.Codex)).not.toContain(NeonModel.Kimi_K3);
+    // Claude on Neon: chat completions only, so OpenCode yes, Codex no.
+    expect(values(Agent.OpenCode)).toContain(NeonModel.Claude_Haiku_4_5);
+    expect(values(Agent.OpenCode)).toContain(NeonModel.Claude_Opus_5_5);
+    expect(values(Agent.Codex).some((v) => v.startsWith("neon/claude-"))).toBe(false);
+  });
+
   it("includes Cursor models", () => {
     const cursorModels = MODEL_OPTIONS_BY_AGENT[Agent.Cursor].flatMap((group) => group.options);
 
diff --git a/packages/cli/src/commands/create-wizard.ts b/packages/cli/src/commands/create-wizard.ts
index cb76520..2de4f1f 100644
--- a/packages/cli/src/commands/create-wizard.ts
+++ b/packages/cli/src/commands/create-wizard.ts
@@ -117,6 +117,14 @@ async function configureAgent(result: Partial<CreateFlags>): Promise<boolean> {
   result.agentModel = model;
   result.agentProvider = provider;
 
+  // Neon runs only with the stored credential (token plus branch gateway URL):
+  // the backend rejects both the Upstash-managed key and a raw key for neon/.
+  if (model.startsWith("neon/")) {
+    result.agentApiKey = "stored";
+    console.log(dim("  Neon AI Gateway uses your stored Neon credential (token and gateway URL)."));
+    return true;
+  }
+
   const keyOption = await interactiveSelect({
     prompt: cyan("Agent API key:"),
     items: API_KEY_OPTIONS,
diff --git a/packages/cli/src/models.ts b/packages/cli/src/models.ts
index b73ab2f..ca09af9 100644
--- a/packages/cli/src/models.ts
+++ b/packages/cli/src/models.ts
@@ -4,6 +4,7 @@ import {
   CursorModel,
   OpenAICodex,
   OpenCodeModel,
+  NeonModel,
   OpenRouterModel,
   VercelModel,
 } from "@upstash/box";
@@ -144,6 +145,25 @@ export const MODEL_OPTIONS_BY_AGENT: Record<
         { value: VercelModel.Claude_Sonnet_4_6, label: "Claude Sonnet 4.6 (Vercel)" },
       ],
     },
+    {
+      // Responses API models only: Codex cannot use Neon's chat-only models.
+      label: "Neon AI Gateway",
+      options: [
+        { value: NeonModel.GPT_6_Astra, label: "GPT-6 Astra (Neon)" },
+        { value: NeonModel.GPT_5_6_Sol, label: "GPT-5.6 Sol (Neon)" },
+        { value: NeonModel.GPT_5_6_Terra, label: "GPT-5.6 Terra (Neon)" },
+        { value: NeonModel.GPT_5_6_Luna, label: "GPT-5.6 Luna (Neon)" },
+        { value: NeonModel.GPT_5_5, label: "GPT-5.5 (Neon)" },
+        { value: NeonModel.GPT_5_5_Pro, label: "GPT-5.5 Pro (Neon)" },
+        { value: NeonModel.GPT_5_4, label: "GPT-5.4 (Neon)" },
+        { value: NeonModel.GPT_5_4_Mini, label: "GPT-5.4 Mini (Neon)" },
+        { value: NeonModel.GPT_5_4_Nano, label: "GPT-5.4 Nano (Neon)" },
+        { value: NeonModel.GPT_5_3_Codex, label: "GPT-5.3 Codex (Neon)" },
+        { value: NeonModel.GPT_5_Mini, label: "GPT-5 Mini (Neon)" },
+        { value: NeonModel.GPT_5_Nano, label: "GPT-5 Nano (Neon)" },
+        { value: NeonModel.Grok_4_6, label: "Grok 4.6 (Neon)" },
+      ],
+    },
   ],
   [Agent.OpenCode]: [
     {
@@ -259,6 +279,46 @@ export const MODEL_OPTIONS_BY_AGENT: Record<
         { value: VercelModel.Grok_4_3, label: "Grok 4.3 (Vercel)" },
       ],
     },
+    {
+      // Chat-completions models only: GPT-5.5 Pro and GPT-5.3 Codex are Responses-only on Neon.
+      label: "Neon AI Gateway",
+      options: [
+        { value: NeonModel.GPT_6_Astra, label: "GPT-6 Astra (Neon)" },
+        { value: NeonModel.GPT_5_6_Sol, label: "GPT-5.6 Sol (Neon)" },
+        { value: NeonModel.GPT_5_6_Terra, label: "GPT-5.6 Terra (Neon)" },
+        { value: NeonModel.GPT_5_6_Luna, label: "GPT-5.6 Luna (Neon)" },
+        { value: NeonModel.GPT_5_5, label: "GPT-5.5 (Neon)" },
+        { value: NeonModel.GPT_5_4, label: "GPT-5.4 (Neon)" },
+        { value: NeonModel.GPT_5_4_Mini, label: "GPT-5.4 Mini (Neon)" },
+        { value: NeonModel.GPT_5_4_Nano, label: "GPT-5.4 Nano (Neon)" },
+        { value: NeonModel.GPT_5_Mini, label: "GPT-5 Mini (Neon)" },
+        { value: NeonModel.GPT_5_Nano, label: "GPT-5 Nano (Neon)" },
+        { value: NeonModel.GPT_OSS_120B, label: "GPT OSS 120B (Neon)" },
+        { value: NeonModel.GPT_OSS_20B, label: "GPT OSS 20B (Neon)" },
+        { value: NeonModel.Gemini_3_6_Flash, label: "Gemini 3.6 Flash (Neon)" },
+        { value: NeonModel.Gemini_3_5_Flash, label: "Gemini 3.5 Flash (Neon)" },
+        { value: NeonModel.Gemini_3_5_Flash_Lite, label: "Gemini 3.5 Flash Lite (Neon)" },
+        { value: NeonModel.Gemini_3_1_Pro, label: "Gemini 3.1 Pro (Neon)" },
+        { value: NeonModel.Grok_4_6, label: "Grok 4.6 (Neon)" },
+        { value: NeonModel.Kimi_K3, label: "Kimi K3 (Neon)" },
+        { value: NeonModel.GLM_5_2, label: "GLM-5.2 (Neon)" },
+        { value: NeonModel.Qwen3_5_122B, label: "Qwen3.5 122B (Neon)" },
+        { value: NeonModel.Llama_4_Maverick, label: "Llama 4 Maverick (Neon)" },
+        { value: NeonModel.Claude_Opus_5_5, label: "Claude Opus 5.5 (Neon)" },
+        { value: NeonModel.Claude_Fable_5_1, label: "Claude Fable 5.1 (Neon)" },
+        { value: NeonModel.Claude_Opus_5, label: "Claude Opus 5 (Neon)" },
+        { value: NeonModel.Claude_Sonnet_5, label: "Claude Sonnet 5 (Neon)" },
+        { value: NeonModel.Claude_Fable_5, label: "Claude Fable 5 (Neon)" },
+        { value: NeonModel.Claude_Opus_4_8, label: "Claude Opus 4.8 (Neon)" },
+        { value: NeonModel.Claude_Opus_4_7, label: "Claude Opus 4.7 (Neon)" },
+        { value: NeonModel.Claude_Sonnet_4_6, label: "Claude Sonnet 4.6 (Neon)" },
+        { value: NeonModel.Claude_Opus_4_6, label: "Claude Opus 4.6 (Neon)" },
+        { value: NeonModel.Claude_Opus_4_5, label: "Claude Opus 4.5 (Neon)" },
+        { value: NeonModel.Claude_Haiku_4_5, label: "Claude Haiku 4.5 (Neon)" },
+        { value: NeonModel.Claude_Sonnet_4_5, label: "Claude Sonnet 4.5 (Neon)" },
+        { value: NeonModel.Claude_Opus_4_1, label: "Claude Opus 4.1 (Neon)" },
+      ],
+    },
   ],
   [Agent.Cursor]: [
     {
diff --git a/packages/python-sdk/CHANGELOG.md b/packages/python-sdk/CHANGELOG.md
index f1dbed9..9158026 100644
--- a/packages/python-sdk/CHANGELOG.md
+++ b/packages/python-sdk/CHANGELOG.md
@@ -4,6 +4,12 @@ All notable changes to `upstash-box` (Python) are documented here.
 
 ## Unreleased
 
+- Add `NeonModel` (Neon AI Gateway, `neon/<neon-short-id>`). `infer_default_provider`
+  routes `neon/gpt-*` to Codex, except `neon/gpt-oss-*`, and every other Neon model
+  (GPT OSS, Claude, Gemini, Llama, Qwen, Kimi, GLM, Grok) to OpenCode.
+  Neon's ``CLAUDE_*`` models run on OpenCode only (chat completions); Box does
+  not run Claude Code with Neon. Neon credentials (token + branch base URL)
+  must be stored via the console or agent-credentials API.
 - Add GPT-6.1 Sol to `OpenAICodex`, `OpenRouterModel`, `VercelModel`, and
   `OpenCodeModel`.
 - Init commands now work on every box, not only keep-alive ones. `create(init_command=...)`
diff --git a/packages/python-sdk/PARITY.md b/packages/python-sdk/PARITY.md
index 20bd5df..d5e1e59 100644
--- a/packages/python-sdk/PARITY.md
+++ b/packages/python-sdk/PARITY.md
@@ -17,7 +17,7 @@ JS `Run`/`StreamRun` → Python `Run`/`StreamRun` (+ `AsyncRun`/`AsyncStreamRun`
 | `BoxError`             | `BoxError`                   |
 | `inferDefaultProvider` | `infer_default_provider`     |
 | `runCustomHarness`     | `run_custom_harness`         |
-| `Agent`, `ClaudeCode`, `OpenAICodex`, `OpenCodeModel`, `OpenRouterModel`, `VercelModel`, `CursorModel`, `BoxApiKey` | same names (str-Enums) |
+| `Agent`, `ClaudeCode`, `OpenAICodex`, `OpenCodeModel`, `OpenRouterModel`, `VercelModel`, `NeonModel`, `CursorModel`, `BoxApiKey` | same names (str-Enums) |
 
 ## `Box` instance methods/properties
 
diff --git a/packages/python-sdk/tests/_async/test_infer_provider.py b/packages/python-sdk/tests/_async/test_infer_provider.py
index 43c0766..e8133c0 100644
--- a/packages/python-sdk/tests/_async/test_infer_provider.py
+++ b/packages/python-sdk/tests/_async/test_infer_provider.py
@@ -35,3 +35,15 @@ def test_custom_prefix():
 
 def test_unknown_defaults_to_claude_code():
     assert infer_default_provider("mystery-model") == Agent.CLAUDE_CODE
+
+
+def test_neon_gpt_prefix_infers_codex():
+    assert infer_default_provider("neon/gpt-5-5") == Agent.CODEX
+    assert infer_default_provider("neon/gpt-5-3-codex") == Agent.CODEX
+
+
+def test_neon_chat_only_models_infer_opencode():
+    assert infer_default_provider("neon/gpt-oss-120b") == Agent.OPEN_CODE
+    assert infer_default_provider("neon/gemini-3-6-flash") == Agent.OPEN_CODE
+    assert infer_default_provider("neon/kimi-k3") == Agent.OPEN_CODE
+    assert infer_default_provider("neon/claude-opus-4-8") == Agent.OPEN_CODE
diff --git a/packages/python-sdk/tests/_async/test_models.py b/packages/python-sdk/tests/_async/test_models.py
index 92edaaa..d7a2d4e 100644
--- a/packages/python-sdk/tests/_async/test_models.py
+++ b/packages/python-sdk/tests/_async/test_models.py
@@ -7,6 +7,7 @@
     CursorModel,
     FinishChunk,
     FinishUsage,
+    NeonModel,
     OpenAICodex,
     OpenCodeModel,
     OpenRouterModel,
@@ -83,6 +84,15 @@ def test_claude_opus_5_model_identifier():
     }
 
 
+def test_neon_model_identifiers_use_short_ids():
+    assert NeonModel.GPT_5_5.value == "neon/gpt-5-5"
+    assert NeonModel.GEMINI_3_6_FLASH.value == "neon/gemini-3-6-flash"
+    assert NeonModel.CLAUDE_HAIKU_4_5.value == "neon/claude-haiku-4-5"
+    for member in NeonModel:
+        assert member.value.startswith("neon/")
+        assert "/" not in member.value[len("neon/") :]
+
+
 def test_box_run_data_fields():
     run = BoxRunData.model_validate(
         {
diff --git a/packages/python-sdk/upstash_box/__init__.py b/packages/python-sdk/upstash_box/__init__.py
index 06e24bf..ff5c26f 100644
--- a/packages/python-sdk/upstash_box/__init__.py
+++ b/packages/python-sdk/upstash_box/__init__.py
@@ -93,6 +93,7 @@
     LogEntry,
     McpServerConfig,
     ModelConfig,
+    NeonModel,
     NetworkPolicy,
     OpenAICodex,
     OpenCodeAgentOptions,
@@ -176,6 +177,7 @@
     "OpenCodeModel",
     "OpenRouterModel",
     "VercelModel",
+    "NeonModel",
     # Config / option types
     "AgentConfig",
     "AgentOptions",
diff --git a/packages/python-sdk/upstash_box/_common.py b/packages/python-sdk/upstash_box/_common.py
index 0881bdd..deba8b6 100644
--- a/packages/python-sdk/upstash_box/_common.py
+++ b/packages/python-sdk/upstash_box/_common.py
@@ -107,6 +107,15 @@ def infer_default_provider(model: str) -> Agent:
         return Agent.CODEX
     if model.startswith("vercel/"):
         return Agent.CLAUDE_CODE
+    # Default routing for Neon AI Gateway (Box does not run Claude Code with Neon).
+    # GPT models default to Codex (Responses API). Every other Neon model defaults
+    # to OpenCode (chat completions), which Neon serves for every text model.
+    # Grok 4.6 is also served on Responses, so Codex can run it when chosen
+    # explicitly; it only defaults to OpenCode here.
+    if model.startswith("neon/gpt-") and not model.startswith("neon/gpt-oss-"):
+        return Agent.CODEX
+    if model.startswith("neon/"):
+        return Agent.OPEN_CODE
     if model.startswith("openrouter/"):
         return Agent.CLAUDE_CODE
     if model.startswith("opencode/"):
diff --git a/packages/python-sdk/upstash_box/types.py b/packages/python-sdk/upstash_box/types.py
index c9c7fd1..ab70a29 100644
--- a/packages/python-sdk/upstash_box/types.py
+++ b/packages/python-sdk/upstash_box/types.py
@@ -145,6 +145,57 @@ class VercelModel(str, Enum):
     GROK_4_20_REASONING = "vercel/spacexai/grok-4.20-reasoning"
 
 
+class NeonModel(str, Enum):
+    """Neon AI Gateway model identifiers (``neon/<neon-short-id>``).
+
+    These run on the Codex harness (Responses API) or the OpenCode harness
+    (chat completions); Box does not run Claude Code with Neon.
+    ``GPT_5_5_PRO`` and ``GPT_5_3_CODEX`` are Responses-only (Codex);
+    the other GPT models and ``GROK_4_6`` run on both; ``GPT_OSS_*``, the
+    ``CLAUDE_*`` models and every other non-OpenAI model except Grok are served
+    through chat completions only (OpenCode).
+    Neon credentials are a token plus a per-branch base URL and must be stored
+    via the console or agent-credentials API; use ``BoxApiKey.STORED_KEY``.
+    """
+
+    GPT_6_ASTRA = "neon/gpt-6-astra"
+    GPT_5_6_SOL = "neon/gpt-5-6-sol"
+    GPT_5_6_TERRA = "neon/gpt-5-6-terra"
+    GPT_5_6_LUNA = "neon/gpt-5-6-luna"
+    GPT_5_5 = "neon/gpt-5-5"
+    GPT_5_5_PRO = "neon/gpt-5-5-pro"
+    GPT_5_4 = "neon/gpt-5-4"
+    GPT_5_4_MINI = "neon/gpt-5-4-mini"
+    GPT_5_4_NANO = "neon/gpt-5-4-nano"
+    GPT_5_3_CODEX = "neon/gpt-5-3-codex"
+    GPT_5_MINI = "neon/gpt-5-mini"
+    GPT_5_NANO = "neon/gpt-5-nano"
+    GPT_OSS_120B = "neon/gpt-oss-120b"
+    GPT_OSS_20B = "neon/gpt-oss-20b"
+    GEMINI_3_6_FLASH = "neon/gemini-3-6-flash"
+    GEMINI_3_5_FLASH = "neon/gemini-3-5-flash"
+    GEMINI_3_5_FLASH_LITE = "neon/gemini-3-5-flash-lite"
+    GEMINI_3_1_PRO = "neon/gemini-3-1-pro"
+    GROK_4_6 = "neon/grok-4-6"
+    KIMI_K3 = "neon/kimi-k3"
+    GLM_5_2 = "neon/glm-5-2"
+    QWEN3_5_122B = "neon/qwen35-122b-a10b"
+    LLAMA_4_MAVERICK = "neon/llama-4-maverick"
+    CLAUDE_OPUS_5_5 = "neon/claude-opus-5-5"
+    CLAUDE_FABLE_5_1 = "neon/claude-fable-5-1"
+    CLAUDE_OPUS_5 = "neon/claude-opus-5"
+    CLAUDE_SONNET_5 = "neon/claude-sonnet-5"
+    CLAUDE_FABLE_5 = "neon/claude-fable-5"
+    CLAUDE_OPUS_4_8 = "neon/claude-opus-4-8"
+    CLAUDE_OPUS_4_7 = "neon/claude-opus-4-7"
+    CLAUDE_SONNET_4_6 = "neon/claude-sonnet-4-6"
+    CLAUDE_OPUS_4_6 = "neon/claude-opus-4-6"
+    CLAUDE_OPUS_4_5 = "neon/claude-opus-4-5"
+    CLAUDE_HAIKU_4_5 = "neon/claude-haiku-4-5"
+    CLAUDE_SONNET_4_5 = "neon/claude-sonnet-4-5"
+    CLAUDE_OPUS_4_1 = "neon/claude-opus-4-1"
+
+
 class OpenCodeModel(str, Enum):
     """OpenCode model identifiers — supports models from multiple providers."""
 
diff --git a/packages/sdk/src/__tests__/infer-runner.test.ts b/packages/sdk/src/__tests__/infer-runner.test.ts
index e8761fe..0afbed2 100644
--- a/packages/sdk/src/__tests__/infer-runner.test.ts
+++ b/packages/sdk/src/__tests__/infer-runner.test.ts
@@ -15,6 +15,22 @@ describe("inferDefaultProvider", () => {
     expect(inferDefaultProvider("vercel/openai/gpt-5.5")).toBe(Agent.Codex);
   });
 
+  it("returns Codex for neon/gpt-* models", () => {
+    expect(inferDefaultProvider("neon/gpt-5-5")).toBe(Agent.Codex);
+    expect(inferDefaultProvider("neon/gpt-5-3-codex")).toBe(Agent.Codex);
+    expect(inferDefaultProvider("neon/gpt-6-astra")).toBe(Agent.Codex);
+  });
+
+  it("defaults every non-GPT neon model to OpenCode", () => {
+    // Chat-completions-only on Neon.
+    expect(inferDefaultProvider("neon/gpt-oss-120b")).toBe(Agent.OpenCode);
+    expect(inferDefaultProvider("neon/gemini-3-6-flash")).toBe(Agent.OpenCode);
+    expect(inferDefaultProvider("neon/kimi-k3")).toBe(Agent.OpenCode);
+    expect(inferDefaultProvider("neon/claude-opus-4-8")).toBe(Agent.OpenCode);
+    // Served on both endpoints; Codex can run it when chosen, but the default is OpenCode.
+    expect(inferDefaultProvider("neon/grok-4-6")).toBe(Agent.OpenCode);
+  });
+
   it("returns OpenCode for opencode/ prefix", () => {
     expect(inferDefaultProvider("opencode/zen-claude-sonnet-4.5")).toBe(Agent.OpenCode);
   });
diff --git a/packages/sdk/src/__tests__/types.test.ts b/packages/sdk/src/__tests__/types.test.ts
index 03bb401..d672cdc 100644
--- a/packages/sdk/src/__tests__/types.test.ts
+++ b/packages/sdk/src/__tests__/types.test.ts
@@ -2,6 +2,7 @@ import { describe, expect, it } from "vitest";
 import {
   ClaudeCode,
   CursorModel,
+  NeonModel,
   OpenAICodex,
   OpenCodeModel,
   OpenRouterModel,
@@ -77,3 +78,24 @@ describe("Claude Opus 5 model identifiers", () => {
     expect(model).toBe(expected);
   });
 });
+
+describe("Neon AI Gateway model identifiers", () => {
+  it.each([
+    [NeonModel.GPT_5_5, "neon/gpt-5-5"],
+    [NeonModel.GPT_5_3_Codex, "neon/gpt-5-3-codex"],
+    [NeonModel.GPT_OSS_120B, "neon/gpt-oss-120b"],
+    [NeonModel.Gemini_3_6_Flash, "neon/gemini-3-6-flash"],
+    [NeonModel.Kimi_K3, "neon/kimi-k3"],
+    [NeonModel.Claude_Opus_5_5, "neon/claude-opus-5-5"],
+    [NeonModel.Claude_Haiku_4_5, "neon/claude-haiku-4-5"],
+  ])("uses Neon's short id under the neon/ namespace: %s", (model, expected) => {
+    expect(model).toBe(expected);
+  });
+
+  it("never carries a provider segment", () => {
+    for (const value of Object.values(NeonModel)) {
+      expect(value.startsWith("neon/")).toBe(true);
+      expect(value.slice("neon/".length)).not.toContain("/");
+    }
+  });
+});
diff --git a/packages/sdk/src/client.ts b/packages/sdk/src/client.ts
index 7109a24..af3dad5 100644
--- a/packages/sdk/src/client.ts
+++ b/packages/sdk/src/client.ts
@@ -111,6 +111,13 @@ export function inferDefaultProvider(model: string): Agent {
   if (model.startsWith("cursor/")) return Agent.Cursor;
   if (model.startsWith("vercel/openai/")) return Agent.Codex;
   if (model.startsWith("vercel/")) return Agent.ClaudeCode;
+  // Default routing for Neon AI Gateway (Box does not run Claude Code with Neon). GPT
+  // models default to Codex (Responses API). Every other Neon model defaults to
+  // OpenCode (chat completions), which Neon serves for every text model. Grok 4.6 is
+  // also served on Responses, so Codex can run it when chosen explicitly; it only
+  // defaults to OpenCode here.
+  if (model.startsWith("neon/gpt-") && !model.startsWith("neon/gpt-oss-")) return Agent.Codex;
+  if (model.startsWith("neon/")) return Agent.OpenCode;
   if (model.startsWith("openrouter/")) return Agent.ClaudeCode;
   if (model.startsWith("opencode/")) return Agent.OpenCode;
   if (model.startsWith("openai/")) return Agent.Codex;
diff --git a/packages/sdk/src/index.ts b/packages/sdk/src/index.ts
index 10e1fa6..13d1627 100644
--- a/packages/sdk/src/index.ts
+++ b/packages/sdk/src/index.ts
@@ -17,6 +17,7 @@ export {
   OpenCodeModel,
   OpenRouterModel,
   VercelModel,
+  NeonModel,
   Agent,
   BoxApiKey,
 } from "./types.js";
diff --git a/packages/sdk/src/types.ts b/packages/sdk/src/types.ts
index c031377..64bbcc2 100644
--- a/packages/sdk/src/types.ts
+++ b/packages/sdk/src/types.ts
@@ -143,6 +143,57 @@ export enum VercelModel {
   Grok_4_20_Reasoning = "vercel/spacexai/grok-4.20-reasoning",
 }
 
+/**
+ * Neon AI Gateway model identifiers — Neon's short model IDs under the `neon/` namespace.
+ *
+ * These models run on the Codex harness (Responses API) or the OpenCode harness
+ * (chat completions). Box does not run Claude Code with Neon.
+ * Codex-only: `GPT_5_5_Pro`, `GPT_5_3_Codex` (Responses-only on Neon).
+ * Both: the other GPT models and `Grok_4_6` (Neon serves them on both endpoints).
+ * OpenCode-only: `GPT_OSS_120B`, `GPT_OSS_20B`, the Claude models and every other
+ * non-OpenAI model except Grok (Neon serves them through chat completions only).
+ * Neon credentials are a token plus a per-branch base URL and must be stored via the
+ * console or agent-credentials API; use `BoxApiKey.StoredKey`.
+ */
+export enum NeonModel {
+  GPT_6_Astra = "neon/gpt-6-astra",
+  GPT_5_6_Sol = "neon/gpt-5-6-sol",
+  GPT_5_6_Terra = "neon/gpt-5-6-terra",
+  GPT_5_6_Luna = "neon/gpt-5-6-luna",
+  GPT_5_5 = "neon/gpt-5-5",
+  GPT_5_5_Pro = "neon/gpt-5-5-pro",
+  GPT_5_4 = "neon/gpt-5-4",
+  GPT_5_4_Mini = "neon/gpt-5-4-mini",
+  GPT_5_4_Nano = "neon/gpt-5-4-nano",
+  GPT_5_3_Codex = "neon/gpt-5-3-codex",
+  GPT_5_Mini = "neon/gpt-5-mini",
+  GPT_5_Nano = "neon/gpt-5-nano",
+  GPT_OSS_120B = "neon/gpt-oss-120b",
+  GPT_OSS_20B = "neon/gpt-oss-20b",
+  Gemini_3_6_Flash = "neon/gemini-3-6-flash",
+  Gemini_3_5_Flash = "neon/gemini-3-5-flash",
+  Gemini_3_5_Flash_Lite = "neon/gemini-3-5-flash-lite",
+  Gemini_3_1_Pro = "neon/gemini-3-1-pro",
+  Grok_4_6 = "neon/grok-4-6",
+  Kimi_K3 = "neon/kimi-k3",
+  GLM_5_2 = "neon/glm-5-2",
+  Qwen3_5_122B = "neon/qwen35-122b-a10b",
+  Llama_4_Maverick = "neon/llama-4-maverick",
+  Claude_Opus_5_5 = "neon/claude-opus-5-5",
+  Claude_Fable_5_1 = "neon/claude-fable-5-1",
+  Claude_Opus_5 = "neon/claude-opus-5",
+  Claude_Sonnet_5 = "neon/claude-sonnet-5",
+  Claude_Fable_5 = "neon/claude-fable-5",
+  Claude_Opus_4_8 = "neon/claude-opus-4-8",
+  Claude_Opus_4_7 = "neon/claude-opus-4-7",
+  Claude_Sonnet_4_6 = "neon/claude-sonnet-4-6",
+  Claude_Opus_4_6 = "neon/claude-opus-4-6",
+  Claude_Opus_4_5 = "neon/claude-opus-4-5",
+  Claude_Haiku_4_5 = "neon/claude-haiku-4-5",
+  Claude_Sonnet_4_5 = "neon/claude-sonnet-4-5",
+  Claude_Opus_4_1 = "neon/claude-opus-4-1",
+}
+
 /**
  * OpenCode model identifiers — supports models from multiple providers
  */
@@ -291,13 +342,13 @@ type HarnessConfig =
     }
   | {
       harness: Agent.Codex;
-      model: OpenAICodex | OpenRouterModel | VercelModel;
+      model: OpenAICodex | OpenRouterModel | VercelModel | NeonModel;
       provider?: never;
       runner?: never;
     }
   | {
       harness: Agent.OpenCode;
-      model: OpenCodeModel | ClaudeCode | OpenAICodex | OpenRouterModel | VercelModel;
+      model: OpenCodeModel | ClaudeCode | OpenAICodex | OpenRouterModel | VercelModel | NeonModel;
       provider?: never;
       runner?: never;
     }
@@ -313,14 +364,14 @@ type HarnessConfig =
   | {
       /** @deprecated Use `harness` instead. */
       provider: Agent.Codex;
-      model: OpenAICodex | OpenRouterModel | VercelModel;
+      model: OpenAICodex | OpenRouterModel | VercelModel | NeonModel;
       harness?: never;
       runner?: never;
     }
   | {
       /** @deprecated Use `harness` instead. */
       provider: Agent.OpenCode;
-      model: OpenCodeModel | ClaudeCode | OpenAICodex | OpenRouterModel | VercelModel;
+      model: OpenCodeModel | ClaudeCode | OpenAICodex | OpenRouterModel | VercelModel | NeonModel;
       harness?: never;
       runner?: never;
     }
@@ -341,7 +392,14 @@ type HarnessConfig =
   | {
       /** @deprecated Use `harness` instead. */
       runner: Exclude<Agent, Agent.Custom>;
-      model: OpenCodeModel | ClaudeCode | OpenAICodex | OpenRouterModel | VercelModel | CursorModel;
+      model:
+        | OpenCodeModel
+        | ClaudeCode
+        | OpenAICodex
+        | OpenRouterModel
+        | VercelModel
+        | NeonModel
+        | CursorModel;
       harness?: never;
       provider?: never;
     }