Megastructure Arc 2.1.4

• Add a Meta Model API key in Settings → Connections & models and run Muse Spark or Muse Wonder as agents. Meta connections default to the Responses API protocol, which keeps each step's reasoning, commentary and completed tool calls in private local state, so an interrupted or restarted agent continues from its last safe step without repeating completed tool calls. OpenAI and custom connections can choose Responses too; existing setups keep their protocol. Thinking gains Extra high and Maximum: Meta models always think and offer Minimal to Extra high, plus Maximum on Muse Spark 1.3 and Muse Wonder 1.0; Anthropic keeps Off to High; other API providers list every level, and Arc sends the chosen level for the provider to accept or refuse.
• Arc's own agents can use the tools of local stdio MCP servers. In Settings → Tools (MCP), add a service, or import one from Claude Code, Cursor, Codex, Gemini or Muse Code without changing their files, and test its catalog; then grant it to an agent under Agent settings… → MCP tools. A service works for an agent in a Full Access room with a project folder, and unsupported remote entries stay disabled. Each agent gets its own connection, with progress, cancellation, Disconnect and Reset. Secrets go to the system credential store, and complete results are kept for the agent to page through or for you to save as an artifact.
• MCP tools read like tools. A service's tools reach the model as <namespace>__<tool>, for example rea__binary_session; the namespace comes from the service label once and never changes, and a short hash is added only when a name would exceed 64 characters or two tool names would read the same. Each service has a connection timeout, 60 seconds by default and up to 600, so a first-run npx -y download has time to finish. A result larger than the model's view arrives as the largest preview that fits, marked incomplete; Arc keeps the whole result with its digest, size, completeness and redaction details, and mcp_output pages through it as text. A call the service reports as failed returns ok: false with error: tool_error. Revoking a grant, or editing or deleting a service, closes its connections in the background without holding up other agents.
• Muse Code, Meta's terminal coding agent, connects to Arc. Its adapter writes an optional stdio entry into Muse's settings.json, so a stopped hub never blocks a Muse run, and Arc Desktop installs it when it starts the local hub and finds Muse's settings folder or the muse command, while Launch automation is on, as it is by default. Install renames a legacy mcp_servers key to mcpServers and keeps its servers; Muse loads no MCP servers while a file has both keys. A Muse adapter you uninstall stays uninstalled, even when your file holds both keys.
• Add agent is a source browser: pick, then confirm. Sources on the left cover recent routes from every room, agents already in the room, each API key, servers, model files, apps and saved setups; the right side lists that source's models with its own search. Choose the count, name, role, behaviours, instructions and folder, then Add, or double-click a model or press Enter to add it at once. Long catalogs fold duplicate variants, keep audio, image and embedding models out of the way, order smaller catalogs by version, and mark free models and models that cannot call tools. Typing an exact model ID selects it, or offers it as typed; changing an agent's model opens on its own key with the current model marked; an app with no profile gets one on its first add. The server and model-file panes offer + Add server and + Add model file, Recent and Pinned end with + Add API key, + Add server and + Add model file, and a model file you add is selected, ready to add or switch to.
• Star a model, saved setup or model file to pin it; pins lead their own source. A key shows its pinned and recently used setups first. Archive hides a setup from every picker without stopping agents that use it, and Tidy up, in the source list, while changing an agent's model and in a key's saved-setups header, suggests duplicate keys, servers and setups, test or agent-made setups, and setups idle for a month or that can no longer start, changing nothing until Apply. A server can be removed only when it lists no models and no agent uses it. arc_list_model_sources returns the pins and asks agents to prefer them when a task names no model; archived setups drop out of it, while arc_list_model_profiles still lists them.
• A command-line agent started in a folder linked to a room joins that room by itself. Its own Arc bridge, in Claude Code, Codex, Cursor, Gemini, Muse Code and the other adapters that start arc mcp per session, redeems the folder's code on the agent's first Arc call that is not a join or a lookup; the room shows that it joined via the linked folder's code, and the result says where. An explicit arc_join wins, and a resumed identity, an unlinked folder or Claude Desktop's shared arc-cowork connection never joins by folder.

• After you change an agent's model from Manage, the composer stays on that agent instead of falling back to the room.
• arc_spawn_agents passes workspace_path through the MCP adapter, so new seats get the folder that was asked for.
• Settings switches whose value comes from the hub or the app, such as Keep local hub running after Arc Desktop quits, no longer show a guess. They rest mid-track and take no clicks until the saved value arrives, arc_ui_command waits up to 1.5 seconds for it, and a value that never arrives is flagged loading in the snapshot. A read that fails leaves the switch loading with Could not load this setting beneath it, where Keep local hub running used to fall back to on and Ask before copying attached files to off.
• A snapshot with a tight max_chars budget keeps the sidebar's Settings button and the Settings menu, and a clipped region's line is marked [+N omitted] so an agent knows to ask for more.
• Snapshots list controls kept from agents, such as License and Security & network, as [operator-only]: named, with no ref or value, and still out of agents' reach.
• Presentation mode hides your home folder in paths. While presenting, message text, inline code, file chips, the room's working-folder tooltip and panel, and an agent's shell and file cards show it as ~. Only the display changes: links and file chips still open the real path.
• API agents no longer hang when a provider keeps a request open with keepalives or a slow drip of whitespace. A streamed reply now ends when no new output (text, reasoning or tool-call arguments) arrives for the Response deadline, 300 seconds by default, or after a hard cap of the larger of one hour and four times that deadline, so a long reply that keeps producing output is not cut off. A reply that arrives in one piece is capped at the Response deadline. The error says which limit ended the reply and, once the request was sent, that Arc did not re-send it. A rate-limit cooldown before listing a provider's models no longer counts against the deadline, and the Agent settings hint explains both cases.
• Repairing an adapter in Settings → Harness adapters now ends an earlier uninstall, as Install does, so Arc keeps the repaired adapter working at later launches.

Windows 10/11 (64-bit), or macOS 11+ on Apple Silicon. Bundled Local AI requires macOS 26+. Computer use requires macOS 14+.