chroma-core/chroma · error · ChromaValueError

Model cannot be updated

Error message

Model cannot be updated

What it means

Thrown as a ChromaValueError by ChromaCloudQwenEmbeddingFunction.validateConfigUpdate() when an update payload contains the key "model". The cloud model is part of the function's identity: vectors already in the collection were produced by that model, so changing it would make the space inconsistent. Updates must not include model.

Source

Thrown at clients/new-js/packages/ai-embeddings/chroma-cloud-qwen/src/index.ts:250

    const serializedInstructions: Record<string, Record<string, string>> = {};
    for (const [taskKey, targets] of Object.entries(this.instructions)) {
      serializedInstructions[taskKey] = {};
      for (const [targetKey, instruction] of Object.entries(targets)) {
        serializedInstructions[taskKey][targetKey] = instruction;
      }
    }

    return {
      model: this.model,
      task: this.task,
      instructions: serializedInstructions as any,
      api_key_env_var: this.apiKeyEnvVar,
    };
  }

  public validateConfigUpdate(newConfig: Record<string, any>): void {
    if ("model" in newConfig) {
      throw new ChromaValueError("Model cannot be updated");
    }

    if ("task" in newConfig) {
      throw new ChromaValueError("Task cannot be updated");
    }

    if ("instructions" in newConfig) {
      throw new ChromaValueError("Instructions cannot be updated");
    }
  }

  public static validateConfig(config: ChromaCloudQwenConfig): void {
    validateConfigSchema(config, NAME);
  }
}

registerEmbeddingFunction(NAME, ChromaCloudQwenEmbeddingFunction);

View on GitHub (pinned to aecdd12c8a)

Solutions

1. Remove "model" from the update payload — it is fixed at creation time.
2. To use a different model, create a new collection with a new embedding function and re-index.
3. Send only genuinely mutable keys in update payloads.

Example fix

// before
await collection.modify({
  embedding_function: { name: "chroma-cloud-qwen", config: { model: "Qwen/Qwen3-Embedding-0.6B", task: null } },
});

// after: create a new collection for a different model
const newCol = await client.createCollection({
  name: "docs-qwen-v2",
  embeddingFunction: new ChromaCloudQwenEmbeddingFunction({
    model: ChromaCloudQwenEmbeddingModel.QWEN3_EMBEDDING_0p6B,
    task: null,
  }),
});

const QWEN_IMMUTABLE = new Set(["model", "task", "instructions"]);
const patch = { ...desiredUpdate };
for (const k of Object.keys(patch)) {
  if (QWEN_IMMUTABLE.has(k)) delete patch[k]; // or throw with a clear message
}
if (Object.keys(patch).length === 0) {
  throw new Error("Nothing updatable in payload; model is fixed at creation");
}

When it happens

Trigger: Attempting to modify the embedding function config with { model: ... } (e.g., via collection modify/config-update flows); submitting a full getConfig() snapshot as an update instead of only mutable fields.

Common situations: Copy-pasting a serialized config into an update call; migrating collections by 'just changing the model', which is not supported; UI/tooling that round-trips whole config objects.

Related errors

• Task cannot be updated
• Instructions cannot be updated
• Config is missing a required field
• The model name cannot be changed after initialization.
• The task type cannot be changed after initialization.

AI-assisted analysis of chroma-core/chroma@aecdd12c8a (2026-08-16). Data as JSON: /api/errors/9e5b6f8d6db3dd7b. Report an issue: GitHub.