fix: surface resolved model limits (#1608)

Signed-off-by: ulofiai <monsterking@tutamail.com>
Co-authored-by: ulofiai <monsterking@tutamail.com>

base-action/src/run-claude-sdk.ts

@@ -82,6 +82,35 @@ async function createPromptConfig(
   return createMultiBlockMessage();
 }
 
+type ModelUsageSummary = Record<
+  string,
+  {
+    contextWindow: number;
+    maxOutputTokens: number;
+  }
+>;
+
+/**
+ * Keep resolved model limits visible without exposing token usage or cost details.
+ */
+function sanitizeModelUsage(
+  modelUsage: SDKResultMessage["modelUsage"] | undefined,
+): ModelUsageSummary | undefined {
+  if (!modelUsage) {
+    return undefined;
+  }
+
+  return Object.fromEntries(
+    Object.entries(modelUsage).map(([model, usage]) => [
+      model,
+      {
+        contextWindow: usage.contextWindow,
+        maxOutputTokens: usage.maxOutputTokens,
+      },
+    ]),
+  );
+}
+
 /**
  * Sanitizes SDK output to match CLI sanitization behavior
  */
@@ -119,6 +148,7 @@ function sanitizeSdkOutput(
         num_turns: resultMsg.num_turns,
         total_cost_usd: resultMsg.total_cost_usd,
         permission_denials_count: resultMsg.permission_denials?.length ?? 0,
+        modelUsage: sanitizeModelUsage(resultMsg.modelUsage),
       },
       null,
       2,

base-action/test/run-claude-sdk.test.ts

@@ -64,6 +64,95 @@ describe("runClaudeWithSdk", () => {
     }
   });
 
+  test("logs resolved model limits without exposing token usage", async () => {
+    const consoleLogSpy = spyOn(console, "log").mockImplementation(() => {});
+
+    tempDir = await mkdtemp(join(tmpdir(), "claude-sdk-"));
+    process.env.RUNNER_TEMP = tempDir;
+
+    const promptPath = join(tempDir, "prompt.txt");
+    await writeFile(promptPath, "test prompt");
+
+    const initMessage = {
+      type: "system",
+      subtype: "init",
+      session_id: "session-123",
+      model: "claude-opus-5",
+    };
+
+    const resultMessage = {
+      type: "result",
+      subtype: "success",
+      is_error: false,
+      duration_ms: 434,
+      num_turns: 1,
+      total_cost_usd: 1.23,
+      permission_denials: [],
+      modelUsage: {
+        "claude-opus-5": {
+          inputTokens: 96209,
+          outputTokens: 55324,
+          cacheReadInputTokens: 1135701,
+          cacheCreationInputTokens: 149043,
+          webSearchRequests: 0,
+          costUSD: 1.23,
+          contextWindow: 200000,
+          maxOutputTokens: 64000,
+        },
+      },
+    };
+
+    mock.module("@anthropic-ai/claude-agent-sdk", () => ({
+      query: async function* () {
+        yield initMessage;
+        yield resultMessage;
+      },
+    }));
+
+    try {
+      const { runClaudeWithSdk } = await import("../src/run-claude-sdk");
+
+      await expect(
+        runClaudeWithSdk(promptPath, {
+          sdkOptions: {},
+          showFullOutput: false,
+          hasJsonSchema: false,
+        }),
+      ).resolves.toMatchObject({ conclusion: "success" });
+
+      const sanitizedResult = consoleLogSpy.mock.calls
+        .map(([message]) => message)
+        .find(
+          (message) =>
+            typeof message === "string" && message.includes('"type": "result"'),
+        );
+
+      expect(sanitizedResult).toBeDefined();
+      if (typeof sanitizedResult !== "string") {
+        throw new Error("Sanitized result output was not logged");
+      }
+      expect(JSON.parse(sanitizedResult)).toEqual({
+        type: "result",
+        subtype: "success",
+        is_error: false,
+        duration_ms: 434,
+        num_turns: 1,
+        total_cost_usd: 1.23,
+        permission_denials_count: 0,
+        modelUsage: {
+          "claude-opus-5": {
+            contextWindow: 200000,
+            maxOutputTokens: 64000,
+          },
+        },
+      });
+      expect(sanitizedResult).not.toContain("inputTokens");
+      expect(sanitizedResult).not.toContain("costUSD");
+    } finally {
+      consoleLogSpy.mockRestore();
+    }
+  });
+
   test("fails when result subtype is success but is_error is true", async () => {
     const consoleErrorSpy = spyOn(console, "error").mockImplementation(
       () => {},

docs/configuration.md

@@ -275,6 +275,29 @@ For provider-specific models:
     # ... other inputs
 ```
 
+### 1M context models through an API gateway
+
+When `ANTHROPIC_BASE_URL` points to an Anthropic-compatible API gateway,
+Claude Code may not be able to verify that the gateway supports a model's native
+1M context window and can budget the session at 200K instead. Append the
+`[1m]` selector to explicitly use the 1M context window for supported models,
+including Claude Opus 5 and Claude Sonnet 5:
+
+```yaml
+- uses: anthropics/claude-code-action@v1
+  with:
+    claude_args: |
+      --model "claude-opus-5[1m]"
+    # ... other inputs
+```
+
+Use the same selector when setting a model through `ANTHROPIC_MODEL` or another
+Claude Code model environment variable. The selector is resolved by Claude Code
+before requests are sent to the provider. The action's sanitized result output
+includes each model's resolved
+`contextWindow` and `maxOutputTokens` under `modelUsage`, so these limits are
+visible without enabling `show_full_output`.
+
 ## Claude Code Settings
 
 You can provide Claude Code settings to customize behavior such as model selection, environment variables, permissions, and hooks. Settings can be provided either as a JSON string or a path to a settings file.