tl;dr: SBCL 2.6.7 adds a new SB-MANUAL contrib module that embeds the manual in docstrings for interactive exploration, extends SB-SIMD to ARM64, and adds AVX512 support on x86-64. The release includes miscellaneous bug fixes (SAP-REF-N on ARM64, MULTIPLE-VALUE-CALL miscompilation, CONCATENATE type errors) and optimizations including SIMD-accelerated UTF-8 conversions, cons-free handling of constant complex numbers in local calls, and a tuned sparse-set implementation in the compiler.