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Xum supports multiple AI providers. Configure provider API keys in Settings → Providers — see Providers for setup.

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First-class Models

Xum ships with curated models kept up to date with the frontier. Use any custom model with /model <provider:model_id>. Xum supports the GPT-6 tiers (GPT-6.1 Sol, GPT-6 Astra, and GPT-6 Luna); older OpenAI GPT models are no longer supported. GPT-6 Luna supports thinking from off through max on the default Responses API route. On the opt-in Chat Completions route, Xum disables its reasoning because OpenAI only supports function calling there with reasoning off. GPT-6.1 Sol (the gpt and sol aliases) and GPT-6 Astra support thinking from low through max; OpenAI does not allow turning their reasoning off. Use the default Responses API route with them, because OpenAI does not support tool calling for these models on Chat Completions.

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OpenAI Ultrafast

To use OpenAI’s fastest processing tier, choose ultrafast as the service tier in Settings → Providers → OpenAI. Xum sends it only to models that OpenAI serves Ultrafast for: GPT-6 Astra. Other models run without a service tier instead of falling back to Fast. Ultrafast costs 6× the Standard price, and Xum’s cost tracking uses that rate. OpenAI says GPT-6.1 Sol Ultrafast will arrive later.

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Pro reasoning mode (GPT-6)

GPT-6.1 Sol, GPT-6 Astra, and GPT-6 Luna support OpenAI’s pro reasoning mode. Open the reasoning selector next to the model picker and enable Pro mode (or run “Toggle Pro Reasoning Mode” from the Command Palette) to send reasoning.mode: "pro" with each request. The setting is saved per workspace. Pro mode can consume more tokens and responses can take noticeably longer. Pro is available on supported direct OpenAI Responses API routes. Gateway routes, Chat Completions, and Codex OAuth use standard mode. For advisor calls, use the Reasoning picker in the Advisor section of Settings → Agents. Advisor Pro mode is saved independently of reasoning effort and the calling chat’s mode.

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Model Selection

Keyboard shortcuts:
  • Cycle models
    • macOS: Cmd+/
    • Windows/Linux: Ctrl+/
To choose a specific model, click the model pill in the chat footer. Alternatively, use the Command Palette (Cmd+Shift+P / Ctrl+Shift+P):
  1. Type “model”
  2. Select “Change Model”
  3. Choose from available models
Models are specified in the format: provider:model-name

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Add custom models

Under Settings → Models, choose a provider and use the Model ID field to search its catalog or enter an ID. Clicking a suggestion, or selecting one with arrow keys and Enter, adds it immediately. Without an explicit selection, Add or Enter adds the ID you typed. Opening the field requests suggestions for the selected provider. Discovery does not add models to your configured list or change routing. You can still enter IDs while suggestions load, when the catalog is empty, or when listing fails.

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Suggestion availability

Bedrock suggestions support configured or environment bearer tokens, explicit AWS keys, and environment AWS keys when no profile is selected. They use standard regional endpoints. Profile-based authentication, SSO, role assumption, credential processes, metadata credentials, and custom endpoints are not supported for suggestions; enter model IDs manually for those configurations. These limits apply to discovery, not to inference. Xum Gateway remains a routing option, not a provider in this field. Configure it through the Route column instead. A catalog entry does not guarantee account access, tool support, or availability through every route. Adding a model is separate from choosing its route; see Providers for routing and credential setup.

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Model fallbacks

When a model refuses to respond, Xum can retry the turn on the next model in that model’s fallback chain. Chains apply only to refusals, never to quota, auth, or network errors. Edit them under Settings → Models → Model Fallbacks, or in ~/.xum/config.json under modelFallbacks. New installs start with these chains: Claude Sonnet 5.5 can refuse some higher-risk cybersecurity requests, and Anthropic’s own fallback for those requests is Claude Sonnet 5. Updates never change an existing config’s chains. If your config predates the Sonnet 5.5 chain, add it by hand:
  1. Under Settings → Models, add the custom model claude-sonnet-5 for Anthropic.
  2. Under Model Fallbacks, add a chain for anthropic:claude-sonnet-5-5 and pick anthropic:claude-sonnet-5.
Or add the entry to ~/.xum/config.json directly:

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One-shot Overrides

Override the model or thinking level for a single message using slash commands. The override applies only to that message — workspace settings stay unchanged.

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Syntax

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Thinking levels

Append +level to any model alias. Levels can be named (off, low, medium/med, high, max) or numeric (0–9). Numeric levels are model-relative — they map to the model’s allowed thinking range:
  • 0 = model’s lowest allowed level (e.g., off for Haiku and Sonnet, low for Opus or Astra)
  • Higher numbers select progressively higher levels, clamped to the model’s maximum
This means /haiku+0 disables thinking while /astra+0 sets thinking to low (Astra’s minimum). Use /+level (no model) to override thinking on the current model: /+0 quick answer

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CLI

The xum run CLI accepts the same thinking levels via --thinking:

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Next Steps

Configure Providers

Set up API keys for Anthropic, OpenAI, Google, and other providers.