[Bug] Claude Code shows 200k context for native OpenAI models (gpt-5.6/5.5): model-info.ts omits contextWindow; NATIVE_GPT56_CONTEXT_WINDOW stale at 372k

[yhong91]

Symptom

When routing Claude Code through opencodex (OCX) to native OpenAI models (gpt-5.6-sol / gpt-5.6-terra / gpt-5.6-luna / gpt-5.5), Claude Code displays a 200k context window for these models instead of their real ChatGPT-subscription-channel value of 272k (confirmed for gpt-5.6 by Codex rust-v0.144.6, see PR openai/codex#34009; gpt-5.5 is also 272k).

200k is Claude Code's built-in fallback when a model entry carries no max_input_tokens. The effect is that auto-compact triggers ~72k too early on these models, wasting real context budget.

Root cause

src/claude/model-info.ts:137 - the native-model discovery row is built without passing contextWindow to modelInfo():

for (const slug of nativeSlugs) {
  const id = idStyle === "readable" ? claudeCodeNativeAlias(slug) : aliasForRoute("native", slug);
  if (seen.has(id)) continue;
  seen.add(id);
  const info = modelInfo(id, `${slug} (native)`, nativeEffectiveLadder(slug), true);   // <-- 4 args, no contextWindow
  out.push(info);
  push1mVariant(info, nativeOpenAiContextWindow(slug));   // <-- uses nativeOpenAiContextWindow here
}

modelInfo() (line 84-94) treats a missing 5th contextWindow arg as undefined, which becomes max_input_tokens: null:

function modelInfo(id, displayName, ladder, imageInput, contextWindow?: number): AnthropicModelInfo {
  return {
    ...
    max_input_tokens: typeof contextWindow === "number" && contextWindow > 0 ? contextWindow : null,
    max_tokens: null,
  };
}

Compare the routed-model row at line 147, which does pass it:

const info = modelInfo(id, `${m.id} (${m.provider})`, ladder, imageInput, m.contextWindow);   // routed: passes contextWindow ✓

So native OpenAI models return max_input_tokens: null to Claude Code while routed models (claude-ocx-volcengine-coding-plan--glm-5.2, etc.) correctly carry their value.

Reproduction

OCX 2.10.2, Claude Code 2.1.220, ANTHROPIC_BASE_URL=http://127.0.0.1:10100.

$ curl -s "http://127.0.0.1:10100/v1/models?ids=cli" -H "anthropic-version: 2023-06-01" | jq '.data[] | select(.id|test("native--gpt-5")) | {id, max_input_tokens, max_tokens}'
{
  "id": "claude-ocx-native--gpt-5.6-sol",
  "max_input_tokens": null,
  "max_tokens": null
}
{
  "id": "claude-ocx-native--gpt-5.6-terra",
  "max_input_tokens": null,
  "max_tokens": null
}
{
  "id": "claude-ocx-native--gpt-5.6-luna",
  "max_input_tokens": null,
  "max_tokens": null
}

Same call for a routed model returns the real window (e.g. claude-ocx-volcengine-coding-plan--glm-5.2 -> max_input_tokens: 1000000), confirming only the native path is affected.

Evidence this is a known value that should be reported

The codebase already injects the gpt-5.6 context window for other clients to avoid exactly this 200k fallback - just not for the Claude Code /v1/models path:

• src/codex/catalog/metadata.ts:56 - export const NATIVE_GPT56_CONTEXT_WINDOW = 372_000; (see "Caveat" below — this value is now stale).
• src/grok/sync.ts:37-43 - comment: "Without it Grok falls back to its own default (200k) and understates models like gpt-5.6-sol, which is 372k." -> injects nativeOpenAiContextWindow(id) for Grok.
• src/server/management/native-integration-routes.ts:412-413 - same comment + same fix for the management/native integration path.

The Grok path (#511) and the native-integration path were both fixed to carry contextWindow; the Claude Code discovery path in model-info.ts appears to have been missed.

Caveat — NATIVE_GPT56_CONTEXT_WINDOW is itself stale (372k → 272k)

While drafting this report I verified the current authoritative value against upstream Codex:

• Codex release rust-v0.144.6 lists under Bug Fixes: "corrected their context windows to 272,000 tokens" (PRs Backport refreshed bundled model metadata to 0.144 openai/codex#33972 and Narrow 0.144 hotfix to GPT-5.6 prompts and context openai/codex#34009).
• PR Narrow 0.144 hotfix to GPT-5.6 prompts and context openai/codex#34009 ("Keep the 272,000-token context and maximum context windows for those three models") — merged 2026-07-18, changes context_window and max_context_window for gpt-5.6 sol/terra/luna to 272,000.
• The 372k figure shipped briefly (~8 hours) after the gpt-5.6 release and was reverted by 0.144.6 because it triggered excessive-usage bugs (community report: r/codex, "GPT-5.6 context reduced to 272k").

So src/codex/catalog/metadata.ts:56 (NATIVE_GPT56_CONTEXT_WINDOW = 372_000) is now stale. The gpt-5.5 entry on line 59 is already 272k and correct; only the gpt-5.6 constant lags. This means the one-line model-info.ts fix below would, as written, inject the stale 372k. The constant should be updated to 272_000 in the same change so the injected value matches the upstream-enforced window.

Suggested fix

Two changes, mirroring line 147 and reusing the same accessor already used on line 139:

-    const info = modelInfo(id, `${slug} (native)`, nativeEffectiveLadder(slug), true);
+    const info = modelInfo(id, `${slug} (native)`, nativeEffectiveLadder(slug), true, nativeOpenAiContextWindow(slug));

plus updating the stale constant:

- export const NATIVE_GPT56_CONTEXT_WINDOW = 372_000;
+ export const NATIVE_GPT56_CONTEXT_WINDOW = 272_000;

nativeOpenAiContextWindow is already imported at line 18. After both changes, /v1/models?ids=cli returns max_input_tokens: 272000 for gpt-5.6-* and 272000 for gpt-5.5, and Claude Code will account the real window instead of the 200k fallback. (Applying only the model-info.ts line without the constant update would inject the stale 372k; the constant fix is required for the value to be correct.)

(No [1m] variant is generated for gpt-5.6 since 272k < 1M - push1mVariant already guards on contextWindow < ONE_MILLION, so this change does not surface a spurious 1M row.)

Environment

• opencodex @bitkyc08/opencodex 2.10.2
• Claude Code 2.1.220 (model = "claude-ocx-native--gpt-5.6-sol", ANTHROPIC_BASE_URL=http://127.0.0.1:10100)
• macOS Darwin 25.5.0

Happy to open a PR if a maintainer confirms the fix direction.

[github-actions]

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[github-actions]

Maintainer decision respected

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