Howto — Run a Haiku Claude Agent via ACP in Obsidian¶

Configure the locally-installed claude-agent-acp adapter to run as a separate Claude agent inside Obsidian's Agent Client plugin, pinned to Haiku, isolated from the default Claude Code instance.

This guide is self-contained — every command, env var, settings field, and config file you need is below.

Why do this¶

Cheap, fast model for low-stakes vault work (triage, formatting, lookups, quick rewrites)
Runs alongside your default Sonnet/Opus instance without overriding global settings
Isolated config dir means experimental tweaks (effort, permissions, allowed tools) don't bleed into your main agent

Background — what the layers do¶

Obsidian Agent Client plugin (ACP client)
        │  spawns process, passes env vars + args
        ▼
claude-agent-acp (locally installed binary)
        │  thin ACP transport adapter; loads SDK
        ▼
Claude Agent SDK (same engine as Claude Code)
        │  reads CLAUDE_CONFIG_DIR/settings.json + env
        ▼
Anthropic API → Haiku 4.5

Key idea: the ACP adapter is transport only. Model selection, effort level, permissions, tool restrictions — all of that uses the standard Claude Code env vars and settings.json, exactly as if you were running Claude Code directly. No ACP-specific config language exists.

Precedence order (highest wins):

Environment variables (set in plugin env block)
--model CLI flag (if plugin allows passing args)
model field in settings.json (resolved via CLAUDE_CONFIG_DIR)
Account default

Setup — 4 steps¶

Step 1: Locate your `claude-agent-acp` binary¶

The path is whatever you installed. Common cases:

Install method	Typical path
npm global	run `which claude-agent-acp` to find it (often `~/.npm-global/bin/claude-agent-acp` or `/usr/local/bin/claude-agent-acp`)
npm local in a project	`<project>/node_modules/.bin/claude-agent-acp`
Cloned from source	`node /path/to/claude-agent-acp/dist/index.js`

Note this absolute path — you'll paste it into the Obsidian plugin in Step 3.

Step 2: Create the isolated Haiku config dir¶

Run in WSL terminal:

mkdir -p /mnt/d/OBS/brncx-skills/99-TMP/claude-haiku-config

Then create /mnt/d/OBS/brncx-skills/99-TMP/claude-haiku-config/settings.json with this content:

{
  "model": "haiku",
  "availableModels": ["haiku", "sonnet"],
  "effortLevel": "low",
  "env": {
    "ANTHROPIC_DEFAULT_HAIKU_MODEL": "claude-haiku-4-5"
  }
}

What each field does:

Field	Purpose
`model: "haiku"`	Active model when the session starts
`availableModels`	Restricts the `/model` picker. Drop `"sonnet"` for Haiku-only
`effortLevel: "low"`	Matches Haiku's fast/cheap intent (note: effort levels currently only affect Opus 4.7/4.6 and Sonnet 4.6 — harmless on Haiku)
`env.ANTHROPIC_DEFAULT_HAIKU_MODEL`	Pins the `haiku` alias to a specific model version so it doesn't drift on future Anthropic releases

Optional fields you might add:

{
  "permissions": {
    "allow": ["Read", "Glob", "Grep"],
    "deny": ["Bash"]
  },
  "statusLine": {
    "type": "command",
    "command": "echo '🟡 HAIKU AGENT'"
  }
}

Step 3: Configure the Obsidian Agent Client plugin¶

Open Obsidian → Settings → Community plugins → Agent Client → (your Claude agent entry, or add a new one).

Field	Value
Name	`Claude Haiku` (or whatever you want shown in the picker)
Command / Path	the absolute path from Step 1
Arguments	(leave empty)
Working directory	usually your vault root: `/mnt/d/OBS/brncx-skills`
Environment variables	see env block below

Env block — one KEY=VALUE per line:

CLAUDE_CONFIG_DIR=/mnt/d/OBS/brncx-skills/99-TMP/claude-haiku-config
ANTHROPIC_MODEL=haiku

Why both: - CLAUDE_CONFIG_DIR — points the SDK at your isolated settings.json so this agent's tweaks don't leak into other Claude Code instances - ANTHROPIC_MODEL=haiku — belt-and-braces; env wins over settings.json on precedence, so even if the config dir isn't picked up, Haiku is still active

Step 4: Restart Obsidian and verify¶

Restart Obsidian (the plugin reads env at process spawn time). Open the Agent Client panel, start a session with the Haiku agent, and run:

Command	What it confirms
`/model`	Active model — should show Haiku
`/status`	Account info + which config file is loaded

If the picker shows Sonnet/Opus instead of Haiku, the plugin isn't passing CLAUDE_CONFIG_DIR through. Two fallbacks:

Fallback A — env-only. Drop CLAUDE_CONFIG_DIR and rely on ANTHROPIC_MODEL=haiku alone. You lose the isolated settings.json, but the model pin works.

Fallback B — wrap in a shell script. If the plugin doesn't expose an env block at all, create /mnt/d/OBS/brncx-skills/99-TMP/SCRIPTS/claude-agent-acp-haiku.sh:

#!/usr/bin/env bash
export CLAUDE_CONFIG_DIR=/mnt/d/OBS/brncx-skills/99-TMP/claude-haiku-config
export ANTHROPIC_MODEL=haiku
exec /absolute/path/to/claude-agent-acp "$@"

Make it executable: chmod +x /mnt/d/OBS/brncx-skills/99-TMP/SCRIPTS/claude-agent-acp-haiku.sh

Point the plugin's Command field at the script instead of the binary.

Run two agents side-by-side¶

Duplicate the agent entry in the Obsidian plugin. Same binary path, different env block:

Agent	`CLAUDE_CONFIG_DIR`	`ANTHROPIC_MODEL`	Use for
Default Sonnet/Opus	(unset — uses your normal config)	(unset)	Real work
Haiku	`…/99-TMP/claude-haiku-config`	`haiku`	Quick tasks, triage, lookups

Each runs as a separate ACP server process — fully isolated, no cross-contamination.

Full env var reference¶

These are the env vars the Claude Agent SDK / Claude Code reads. Set any of them in the Obsidian plugin's env block:

Variable	Effect
`ANTHROPIC_MODEL`	Active model alias or full ID (`haiku`, `sonnet`, `opus`, `claude-haiku-4-5`, `claude-opus-4-7[1m]`, etc.)
`ANTHROPIC_DEFAULT_HAIKU_MODEL`	What the `haiku` alias resolves to
`ANTHROPIC_DEFAULT_SONNET_MODEL`	What the `sonnet` alias resolves to
`ANTHROPIC_DEFAULT_OPUS_MODEL`	What the `opus` alias resolves to
`CLAUDE_CONFIG_DIR`	Path to a folder containing settings.json (isolates from default config)
`CLAUDE_CODE_EFFORT_LEVEL`	`low` / `medium` / `high` / `xhigh` / `max` / `auto` (Opus 4.7/4.6, Sonnet 4.6 only)
`CLAUDE_CODE_SUBAGENT_MODEL`	Model used by spawned subagents
`CLAUDE_CODE_DISABLE_1M_CONTEXT`	Set `1` to remove 1M context options from picker
`DISABLE_PROMPT_CACHING`	Set `1` to disable prompt caching globally
`DISABLE_PROMPT_CACHING_HAIKU`	Set `1` to disable prompt caching for Haiku only
`ANTHROPIC_BASE_URL`	Custom API endpoint (LLM gateway, Bedrock proxy, etc.)
`ANTHROPIC_CUSTOM_MODEL_OPTION`	Adds a custom entry to the `/model` picker

Deprecated: ANTHROPIC_SMALL_FAST_MODEL — use ANTHROPIC_DEFAULT_HAIKU_MODEL instead.

Full settings.json reference¶

Fields you can add to the settings.json under CLAUDE_CONFIG_DIR:

{
  "model": "haiku",
  "availableModels": ["haiku", "sonnet"],
  "effortLevel": "low",
  "env": {
    "ANTHROPIC_DEFAULT_HAIKU_MODEL": "claude-haiku-4-5"
  },
  "permissions": {
    "allow": ["Read", "Glob", "Grep", "Edit"],
    "deny": ["Bash(rm *)", "Bash(git push *)"]
  },
  "modelOverrides": {
    "claude-haiku-4-5": "your-custom-id-or-arn"
  },
  "statusLine": {
    "type": "command",
    "command": "/path/to/statusline-script.sh"
  }
}

Field	Purpose
`model`	Initial model on session start
`availableModels`	Allowlist for the `/model` picker; merges across user/project/managed settings
`effortLevel`	Default reasoning effort
`env`	Extra env vars applied when this config is loaded
`permissions.allow` / `permissions.deny`	Tool allowlist / denylist (supports patterns like `Bash(git push *)`)
`modelOverrides`	Map Anthropic model IDs to provider-specific IDs (Bedrock ARNs, Vertex names)
`statusLine`	Custom status line shown above the prompt

Model alias quick reference¶

Alias	Resolves to (Anthropic API)
`haiku`	Claude Haiku 4.5
`sonnet`	Claude Sonnet 4.6
`opus`	Claude Opus 4.7
`sonnet[1m]`	Sonnet 4.6 with 1M context
`opus[1m]`	Opus 4.7 with 1M context
`opusplan`	Opus in plan mode → Sonnet in execution
`default`	Resolves to your account's tier default
`best`	Currently equivalent to `opus`

Troubleshooting¶

Symptom	Fix
`/model` shows Sonnet/Opus, not Haiku	Plugin not passing env. Use Fallback B (shell-script wrapper)
Picker is empty / picker shows wrong models	Check `availableModels` in settings.json — array might be too restrictive
Adapter fails to start	Run the binary path manually in a terminal — confirms it works outside Obsidian
Settings changes don't apply	Restart Obsidian — the ACP server only reads config at spawn time
Both agents share state	They shouldn't if `CLAUDE_CONFIG_DIR` is different — verify by running `/status` in each
Effort level setting ignored	Effort only affects Opus 4.7/4.6 and Sonnet 4.6 — Haiku doesn't support it

References¶

Claude Code model configuration: https://code.claude.com/docs/en/model-config
claude-agent-acp repo: https://github.com/agentclientprotocol/claude-agent-acp
ACP protocol spec: https://agentclientprotocol.com