A relatively-new steel from Carpenter Steels, designed to be nearly identical to GIN-1/G-2.
Sal Glesser posted on BladeForums.com in 2010:
"Another steel that was specially formulated to our request is Carpenter steel's new CTS-BD1. This is, in my opinion, an optimal formualtion for a blade steel. It is based on Hitachi's well known "Gingami I" (silver paper), also knows as G2 (early Spyderco's) and GIN 1 (current Spyderco's). CTS-BD1 has been "tweaked" by Carpenter's metallurgist, Rick Gleixner and the result is very nice, and USA made." 
CTS-BD1 consists of:
Some information from the Spyderco website:
High-performance American-made blade steels are propelling the quality and performance of today's knives to new and higher levels. A U.S.A company called Carpenter Steel recently entered the knife making arena, cutlery people noticed. Carpenter isn't a newcomer to alloy manufacturing just a new-neighbor in the community of blade steel manufacturing and they're launching a new family of alloys called CTS™ steels specifically for cutlery. One of those is CTS-BD1. CTS-BD1 is patterned on Gingami I (also known as G2), the gold-standard for Japanese cutlerers. Its superior edge retention and surface finish are machined to a fine edge and it heat-treats consistently.
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