diff --git a/Cargo.toml b/Cargo.toml
index ef8f9c9a0..1bc4d6b0d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -120,7 +120,7 @@ edition = "2021"
 license = "MIT"
 repository = "https://github.com/paiml/aprender"
 authors = ["Noah Gift <noah@paiml.com>"]
-rust-version = "1.89"
+rust-version = "1.91"
 keywords = ["machine-learning", "inference", "training", "gpu", "simd"]
 categories = ["science", "algorithms"]
 homepage = "https://github.com/paiml/aprender"
@@ -476,7 +476,7 @@ semicolon_if_nothing_returned = "allow"  # Style preference
 name = "aprender"
 version = "0.59.0"
 edition = "2021"
-rust-version = "1.89"
+rust-version = "1.91"
 authors = ["Noah Gift <noah@paiml.com>"]
 license = "MIT"
 description = "Next-generation ML framework in pure Rust — `cargo install aprender` for the `apr` CLI"
diff --git a/crates/apr-cli/Cargo.toml b/crates/apr-cli/Cargo.toml
index ba0134b16..1c78b5833 100644
--- a/crates/apr-cli/Cargo.toml
+++ b/crates/apr-cli/Cargo.toml
@@ -2,7 +2,7 @@
 name = "apr-cli"
 version.workspace = true
 edition = "2021"
-rust-version = "1.89"
+rust-version = "1.91"
 authors = ["Noah Gift <noah@paiml.com>"]
 license = "MIT"
 description = "CLI tool for APR model inspection, debugging, and operations"
diff --git a/crates/apr-format/Cargo.toml b/crates/apr-format/Cargo.toml
index f684e405c..99d5cfcf3 100644
--- a/crates/apr-format/Cargo.toml
+++ b/crates/apr-format/Cargo.toml
@@ -2,7 +2,7 @@
 name = "apr-format"
 version.workspace = true
 edition = "2021"
-rust-version = "1.89"
+rust-version = "1.91"
 description = "Sovereign `.apr` model container format (read + write, v1 APRN + v2 APR\\0) — zero ML/GPU/tokenizer dependencies"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/paiml/aprender"
diff --git a/crates/aprender-cgp/Cargo.toml b/crates/aprender-cgp/Cargo.toml
index b4c818e8e..ff950b54d 100644
--- a/crates/aprender-cgp/Cargo.toml
+++ b/crates/aprender-cgp/Cargo.toml
@@ -2,7 +2,7 @@
 name = "aprender-cgp"
 version.workspace = true
 edition = "2021"
-rust-version = "1.89"
+rust-version = "1.91"
 authors = ["Pragmatic AI Labs"]
 license = "MIT"
 description = "Compute-GPU-Profile: Unified performance analysis CLI for scalar, SIMD, wgpu, and CUDA workloads"
diff --git a/crates/aprender-compute/Cargo.toml b/crates/aprender-compute/Cargo.toml
index 781ca4415..b1e8e86f4 100644
--- a/crates/aprender-compute/Cargo.toml
+++ b/crates/aprender-compute/Cargo.toml
@@ -7,7 +7,7 @@
 name = "aprender-compute"
 version.workspace = true
 edition.workspace = true
-rust-version = "1.89"
+rust-version = "1.91"
 authors.workspace = true
 license.workspace = true
 description = "High-performance SIMD compute library with GPU support, LLM inference engine, and GGUF model loading (was: trueno)"
diff --git a/crates/aprender-core/Cargo.toml b/crates/aprender-core/Cargo.toml
index 134dd60e8..9034bc9dc 100644
--- a/crates/aprender-core/Cargo.toml
+++ b/crates/aprender-core/Cargo.toml
@@ -2,7 +2,7 @@
 name = "aprender-core"
 version.workspace = true
 edition = "2021"
-rust-version = "1.89"
+rust-version = "1.91"
 authors = ["Noah Gift <noah@paiml.com>"]
 license = "MIT"
 description = "Next-generation machine learning library in pure Rust"
diff --git a/crates/aprender-gemm-codegen/Cargo.toml b/crates/aprender-gemm-codegen/Cargo.toml
index a56f0ed23..7518d0300 100644
--- a/crates/aprender-gemm-codegen/Cargo.toml
+++ b/crates/aprender-gemm-codegen/Cargo.toml
@@ -2,7 +2,7 @@
 name = "aprender-gemm-codegen"
 version.workspace = true
 edition = "2021"
-rust-version = "1.89"
+rust-version = "1.91"
 authors = ["Pragmatic AI Labs"]
 license = "MIT"
 description = "Compile-time GEMM microkernel code generation for trueno (sovereign, no external BLAS)"
diff --git a/crates/aprender-serve/Cargo.toml b/crates/aprender-serve/Cargo.toml
index 4883c4944..ebabf7c53 100644
--- a/crates/aprender-serve/Cargo.toml
+++ b/crates/aprender-serve/Cargo.toml
@@ -5,7 +5,7 @@ name = "aprender-serve"
 version.workspace = true
 edition = "2021"
 autobins = false
-rust-version = "1.89"
+rust-version = "1.91"
 authors = ["Pragmatic AI Labs <contact@paiml.com>"]
 license = "MIT"
 description = "Pure Rust ML inference engine built from scratch - model serving for GGUF and safetensors"
diff --git a/scripts/check_msrv.sh b/scripts/check_msrv.sh
new file mode 100755
index 000000000..6a214a930
--- /dev/null
+++ b/scripts/check_msrv.sh
@@ -0,0 +1,34 @@
+#!/usr/bin/env bash
+# check_msrv.sh — verify the workspace actually builds on its DECLARED MSRV.
+#
+# PMAT-MSRV-GATE-001 (Fable rank-14). The declared `rust-version` had silently
+# drifted: Cargo.toml claimed 1.89 while `pmcp` and `wasmtime` transitively require
+# rustc 1.91, and rust-toolchain.toml pins 1.93 — so NOTHING ever verified the claim.
+# This script is the gate: it reads the declared MSRV and compiles the whole
+# workspace on exactly that toolchain, failing loudly on any drift.
+#
+# RED-turning mutation: set rust-version back to "1.89" and re-run — this fails with
+#   `error: rustc 1.89.0 is not supported by pmcp@2.9.0 (requires 1.91)`.
+#
+# Usage:  bash scripts/check_msrv.sh
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+MSRV="$(grep -m1 '^rust-version' Cargo.toml | grep -oE '[0-9]+\.[0-9]+(\.[0-9]+)?')"
+[ -n "$MSRV" ] || { echo "check_msrv: could not read rust-version from Cargo.toml" >&2; exit 2; }
+echo "Declared MSRV (Cargo.toml rust-version): $MSRV"
+
+if ! rustup toolchain list 2>/dev/null | grep -q "^${MSRV}"; then
+  echo "Installing rust ${MSRV} toolchain ..."
+  rustup toolchain install "${MSRV}" --profile minimal --no-self-update
+fi
+
+echo "→ cargo +${MSRV} check --workspace"
+if cargo "+${MSRV}" check --workspace; then
+  echo "✓ workspace builds on its declared MSRV ${MSRV}"
+else
+  echo "✗ MSRV DRIFT: workspace does NOT build on declared rust-version ${MSRV}." >&2
+  echo "  Fix: bump rust-version in Cargo.toml to the true minimum, or pin the" >&2
+  echo "  offending dependency to a version that supports ${MSRV}." >&2
+  exit 1
+fi