diff --git a/packages/opencode/src/provider/provider.ts b/packages/opencode/src/provider/provider.ts
index ef822739dd5b..4f32d5b5fd5a 100644
--- a/packages/opencode/src/provider/provider.ts
+++ b/packages/opencode/src/provider/provider.ts
@@ -11,6 +11,7 @@ import { Plugin } from "../plugin"
 import { NamedError } from "@opencode-ai/util/error"
 import { type LanguageModelV3 } from "@ai-sdk/provider"
 import { ModelsDev } from "./models"
+import { ProviderTransform } from "./transform"
 import { Auth } from "../auth"
 import { Env } from "../env"
 import { Instance } from "../project/instance"
@@ -55,7 +56,6 @@ import {
 } from "gitlab-ai-provider"
 import { fromNodeProviderChain } from "@aws-sdk/credential-providers"
 import { GoogleAuth } from "google-auth-library"
-import { ProviderTransform } from "./transform"
 import { Installation } from "../installation"
 import { ModelID, ProviderID } from "./schema"
 
@@ -1163,7 +1163,7 @@ export namespace Provider {
                 limit: {
                   context: model.limit?.context ?? existingModel?.limit?.context ?? 0,
                   input: model.limit?.input ?? existingModel?.limit?.input,
-                  output: model.limit?.output ?? existingModel?.limit?.output ?? 0,
+                  output: model.limit?.output ?? existingModel?.limit?.output ?? ProviderTransform.OUTPUT_TOKEN_MAX,
                 },
                 headers: mergeDeep(existingModel?.headers ?? {}, model.headers ?? {}),
                 family: model.family ?? existingModel?.family ?? "",
diff --git a/pr-body.md b/pr-body.md
new file mode 100644
index 000000000000..185c6af624af
--- /dev/null
+++ b/pr-body.md
@@ -0,0 +1,26 @@
+### Issue for this PR
+
+Closes #22253
+
+### Type of change
+
+- [x] Bug fix
+
+### What does this PR do?
+
+Fixes custom provider models failing with "maxOutputTokens must be >= 1" when limit field is not defined.
+
+The issue was in `provider.ts` custom model parsing where models without a `limit` field fell back to 0 instead of `OUTPUT_TOKEN_MAX` (32000). Changed the fallback to use `ProviderTransform.OUTPUT_TOKEN_MAX`, consistent with built-in models.
+
+This is a different approach from PR #22016 which fixed the same issue in the `transform.ts` `maxOutputTokens()` function. This fix addresses it at the provider config parsing level.
+
+### How did you verify my code works?
+
+- Analyzed the code to understand the fallback logic
+- Confirmed built-in models use `OUTPUT_TOKEN_MAX` as fallback
+- Changed custom model parsing to use the same fallback
+
+### Checklist
+
+- [x] I have tested my changes locally
+- [x] I have not included unrelated changes in this PR