diff --git a/.gitignore b/.gitignore
index 8e7452683..eae60b8f5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -17,3 +17,17 @@ cmd/cue/cue
 # Note that CI requires a clean git repo when it finishes,
 # so we don't want it to think the credentials file is untracked.
 gha-creds-*.json
+
+# OpenSpec Tooling (Local only)
+openspec/
+
+# Cursor IDE
+.cursor/
+
+# AI Agent Skills/Commands (generated by OpenSpec)
+.claude/skills/openspec-*/
+.claude/commands/opsx/
+.codex/
+.gemini/
+.github/prompts/opsx-*.prompt.md
+.github/skills/openspec-*/
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 66e8d5170..a3a5332a0 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -595,6 +595,42 @@ free to write a comment in GerritHub or GitHub requesting submission.
 This section collects a number of other comments that are outside the
 issue/edit/code review/submit process itself.
 
+### AI-assisted development with OpenSpec
+
+Contributors can optionally use [OpenSpec](https://github.com/Fission-AI/OpenSpec/)
+for AI-assisted development. OpenSpec provides a structured workflow for creating
+proposals, designs, specs, and implementation tasks with AI coding assistants like
+Claude Code, GitHub Copilot, Gemini, and others.
+
+**Setup:**
+
+1. Install OpenSpec CLI (requires Node.js 20.19.0+):
+   ```console
+   $ npm install -g @fission-ai/openspec@latest
+   ```
+
+2. Run the setup script from the repository root:
+   ```console
+   $ ./_scripts/setup-openspec.sh
+   ```
+
+This creates local-only tooling files (gitignored) while specs and context are
+tracked in `doc/`:
+
+- `doc/specs/` - Main specs (source of truth, tracked)
+- `doc/context/` - Shared context like language change checklists (tracked)
+- `openspec/` - Workflow state and config (local only, gitignored)
+
+**Quick start commands** (in your AI assistant):
+- `/opsx:new` - Start a new change with proposal → design → specs → tasks workflow
+- `/opsx:continue` - Continue working on an existing change
+- `/opsx:apply` - Implement tasks from a change
+
+**Updating after OpenSpec upgrades:**
+```console
+$ ./_scripts/setup-openspec.sh update
+```
+
 ### Copyright headers
 
 Files in the CUE repository don't list author names, both to avoid clutter and
diff --git a/_scripts/setup-openspec.sh b/_scripts/setup-openspec.sh
new file mode 100755
index 000000000..1404d5772
--- /dev/null
+++ b/_scripts/setup-openspec.sh
@@ -0,0 +1,111 @@
+#!/bin/bash
+# Setup OpenSpec tooling for local development
+#
+# This script initializes the OpenSpec workflow with configurations
+# pointing to the tracked doc/ directory for specs and context.
+#
+# PREREQUISITES
+# =============
+# Node.js 20.19.0 or higher is required.
+#
+# INSTALLATION
+# ============
+# Install OpenSpec CLI via npm:
+#
+#   npm install -g @fission-ai/openspec@latest
+#
+# For more info: https://github.com/Fission-AI/OpenSpec/
+#
+# USAGE
+# =====
+#   ./_scripts/setup-openspec.sh         # First-time setup
+#   ./_scripts/setup-openspec.sh update  # Regenerate skills after OpenSpec upgrade
+#
+# WHAT IT CREATES (all gitignored)
+# ================================
+# - openspec/config.yaml - OpenSpec configuration
+# - .claude/commands/opsx/* - Claude Code commands
+# - .claude/skills/openspec-*/* - Claude Code skills
+# - Similar for .codex/, .gemini/, .github/ integrations
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
+
+cd "$REPO_ROOT"
+
+MODE="$1"
+
+echo "Setting up OpenSpec tooling..."
+
+# Create openspec directory structure
+mkdir -p openspec
+
+# Create or update config.yaml pointing to doc/
+if [[ ! -f openspec/config.yaml ]] || [[ $MODE != "update" ]]; then
+    cat > openspec/config.yaml <<-'EOF'
+	schema: spec-driven
+
+	# Path to main specs (the source of truth)
+	specsPath: doc/specs
+
+	# Project context (optional)
+	# This is shown to AI when creating artifacts.
+	# Add your tech stack, conventions, style guides, domain knowledge, etc.
+	context: |
+	  Please refer to doc/context/language-features.md for language rules and the
+	  comprehensive checklist for implementing language changes.
+
+	# Per-artifact rules (optional)
+	# Add custom rules for specific artifacts.
+	# Example:
+	#   rules:
+	#     proposal:
+	#       - Keep proposals under 500 words
+	#       - Always include a "Non-goals" section
+	#     tasks:
+	#       - Break tasks into chunks of max 2 hours
+	EOF
+    echo "Created openspec/config.yaml"
+else
+    echo "Keeping existing openspec/config.yaml"
+fi
+
+# Check if openspec CLI is available
+if command -v openspec &> /dev/null; then
+    if [[ $MODE == "update" ]]; then
+        echo "Running 'openspec update' to regenerate AI agent skills..."
+        openspec update
+    else
+        echo "Running 'openspec init' to generate AI agent skills..."
+        # Use --tools to run non-interactively; config.yaml already exists
+        openspec init --tools claude,codex,gemini,github-copilot
+    fi
+else
+    echo ""
+    echo "ERROR: 'openspec' CLI not found."
+    echo ""
+    echo "Install OpenSpec first (requires Node.js 20.19.0+):"
+    echo "  npm install -g @fission-ai/openspec@latest"
+    echo ""
+    echo "For more info: https://github.com/Fission-AI/OpenSpec/"
+    echo ""
+    echo "Then re-run this script."
+    exit 1
+fi
+
+echo ""
+echo "Setup complete!"
+echo ""
+echo "Directory structure:"
+echo "  doc/specs/          - Main specs (tracked, source of truth)"
+echo "  doc/context/        - Shared context files (tracked)"
+echo "  openspec/            - Workflow state and config (local only, gitignored)"
+echo ""
+echo "Quick start:"
+echo "  /opsx:new        - Start a new change"
+echo "  /opsx:continue   - Continue working on a change"
+echo "  /opsx:apply      - Implement tasks from a change"
+echo ""
+echo "Run './_scripts/setup-openspec.sh update' after upgrading OpenSpec."
diff --git a/doc/context/language-features.md b/doc/context/language-features.md
new file mode 100644
index 000000000..5331bacd9
--- /dev/null
+++ b/doc/context/language-features.md
@@ -0,0 +1,103 @@
+# Language Features Context
+
+This is the CUE language repository.
+
+## Language Version Gating
+
+- New language features MUST be gated on a minimum language version
+- Features should specify the minimum version (e.g., v0.16.0) in the design
+- Implementation should check c.experiments.LanguageVersion() and use semver.Compare
+- Error message format: "feature X requires language version vX.Y.Z or later; current version is vA.B.C"
+- The version check should be in internal/core/compile/compile.go
+- See verifyVersion() for the pattern used for builtins
+
+## Experiments
+
+- New language features are often introduced as experiments before becoming stable
+- Experiments are defined in internal/cueexperiment/file.go as fields on the File struct
+- Each experiment has a tag: `experiment:"preview:vX.Y.Z"` (when introduced) and optionally `stable:vX.Y.Z` (when graduated)
+- Users enable experiments via @experiment(name) attribute in CUE files
+- Check experiments via c.experiments.FieldName in the compiler
+- Consider using experiments for features that may need refinement based on user feedback
+
+## Language Change Checklist
+
+When adding new syntax or AST nodes to the CUE language, the following
+packages and files typically need updates. Use this as a comprehensive
+checklist when planning tasks:
+
+### 1. Lexer & Token (cue/token/)
+- [ ] token.go: Add new token constants
+- [ ] token.go: Add keywords to keyword map if applicable
+
+### 2. AST (cue/ast/)
+- [ ] ast.go: Add new AST node struct(s)
+- [ ] ast.go: Implement marker methods (e.g., clauseNode(), exprNode())
+- [ ] ast.go: Add fields to existing structs if extending them
+- [ ] walk.go: Add case for new node type in Walk function
+
+### 3. Parser (cue/parser/)
+- [ ] parser.go: Add parsing logic for new syntax
+- [ ] parser_test.go: Add parser tests
+
+### 4. AST Utilities (cue/ast/astutil/)
+- [ ] apply.go: Add case for new node type in Apply function
+- [ ] resolve.go: Handle new node in scope resolution if it affects scoping
+
+### 5. AST Debug (internal/astinternal/)
+- [ ] debug.go: Add case in DebugStr for new node type
+
+### 6. Compiler - ADT Structures (internal/core/adt/)
+- [ ] expr.go: Add ADT struct for new construct
+- [ ] expr.go: Add fields to existing ADT structs if extending them
+
+### 7. Compiler - Compilation (internal/core/compile/)
+- [ ] compile.go: Add compilation logic for AST to ADT conversion
+- [ ] compile.go: Add language version check if feature-gated
+
+### 8. Evaluator (internal/core/adt/)
+- [ ] Add evaluation logic in appropriate files (e.g., comprehension.go)
+
+### 9. Debug Output (internal/core/debug/)
+- [ ] debug.go: Add case for new ADT node type
+- [ ] compact.go: Add case for new ADT node type
+
+### 10. Walker (internal/core/walk/)
+- [ ] walk.go: Add case for new ADT node type
+
+### 11. Exporter (internal/core/export/)
+- [ ] adt.go: Add export logic for new ADT node to AST conversion
+
+### 12. Dependency Analysis (internal/core/dep/)
+- [ ] dep.go: Handle new construct in dependency marking
+- [ ] mixed.go: Handle new construct if applicable
+
+### 13. Formatter (cue/format/)
+- [ ] node.go: Add formatting logic for new AST node
+
+### 14. Subsumer (internal/core/subsume/)
+- [ ] structural.go: Handle new construct if it affects subsumption
+
+### 15. Tests
+- [ ] cue/testdata/: Add evaluation tests (.txtar files)
+- [ ] cue/parser/parser_test.go: Add parser tests
+- [ ] internal/core/dep/testdata/: Add dependency tracking tests
+- [ ] internal/core/export/testdata/main/: Add export tests
+
+### 16. Documentation
+- [ ] doc/ref/spec.md: Update grammar
+- [ ] doc/ref/spec.md: Add examples
+- [ ] doc/ref/spec.md: Document semantics and scoping rules
+
+### 17. Experiments (if feature is experimental)
+- [ ] internal/cueexperiment/file.go: Add experiment field with tags
+- [ ] internal/core/compile/compile.go: Check experiment flag before enabling
+- [ ] doc/: Document experiment and how to enable it
+- [ ] Consider preview/stable version tags for gradual rollout
+
+### 18. Other Potential Updates
+- [ ] cue/load/tags.go: If feature interacts with build tags
+- [ ] internal/encoding/: If feature affects encoding/decoding
+- [ ] internal/lsp/: If feature needs LSP support
+- [ ] tools/fix/fix.go: If feature needs migration tooling
+- [ ] tools/trim/: If feature affects trimming