Ashkenazi Y-DNA Haplogroup I

Based upon the methodology posted here and using the sample set described here, as of January 2019 it appears that there are three Y-DNA lines in haplogroup I in the Ashkenazi Jewish population: (1) the I-Y11261 subcluster of I-S23612; (2) I-Y23612; and (3) I-Y23115.  Trees for each of those clusters are posted below.

I-S23612 (I-Y11261 subcluster)
Upstream SNPs: 
M170>P215>CTS2257>L460>P214>M223>CTS616>CTS10057>L702>P78>S25733>A427 >S23612
ISOGG Tree (2019): I2a1b1a2a1a1a
TMRCA (YFull Tree)
Y4884: 4,000 ybp (3,300-4,800 ybp @95%) (I-Y4884 is at the same level as S23612)
Y6396: 3,200 ybp (3,300-4,000 ybp @95%) (I-Y6396 is at the same level as I-Y6406)
Y12611: 2,200 ybp (1,500 ybp-3,000 ybp)
Y52940: 1,050 ybp (600-1,750 ybp @94%) (I-Y52940 is at the same level as I-Y50708)
TMRCA (JewishDNA.net)
I-P215 (AB-087): 1,211-1,515 CE (95%)

Here, the I-Y11261 branch and its I-Y50708 subbranch appear to be Ashkenazi, while the upstream branches include almost no men in the sample set.  (The two I-S23612 men in the sample set presumably did not do Big Y testing; Big Y testing would likely put them in the I-Y11261 cluster.)  

The I-Y11261 cluster appears to follow the same pattern as many of the larger Ashkenazi clusters, with (1) a shared direct male ancestor dating back to about the second half of the first millenium CE, as evidenced by initial branching during that time frame; and ((2) substantial branching within those subbranches that presumably dates back to the time when the Ashkenazi population began its massive expansion out of a small bottlenecked population, about 700 to 1,000 years ago.  

I-Y23115
Upstream SNPs: 
M170>P215>CTS2257>L460>P37>M423>CTS5375>L621>CTS10936>S19848>CTS4002 >CTS10228>S20602>Y18331>A2512>A10959>Y23115
ISOGG Tree (2019): Not on ISOGG tree
TMRCA (YFull Tree)
1,000 ybp (600-1,500 ybp @95%)
TMRCA (JewishDNA.net)
I-P215 (AB-087): 1,211-1,515 CE (95%)

The I-Y23115 cluster follows the same pattern as many of the larger Ashkenazi clusters, with (1) a shared direct male ancestor dating back to about the second half of the first millenium CE, as evidenced by initial branching during that time frame; and (2) substantial branching within those subbranches that presumably dates back to the time when the Ashkenazi population began its massive expansion out of a small bottlenecked population, about 700 to 1,000 years ago.  

I-BY424
Upstream SNPs: 
M170>P215>CTS2257>L596>BY421>Z26403>BY424
TMRCA (YFull Tree)
?
TMRCA (JewishDNA.net)
I-P215 (AB-087): 1,211-1,515 CE (95%)

Absent test results showing Ashkenazi branching in this line, it is not possible to make a determination as to when -- or if -- the I-BY424 line became an Ashkenazi Y-DNA line.

Y-DNA SNPs Not Appearing on Trees Posted Above
In addition to the SNPs posted above, there are a number of SNPs identified through the methodology used on this website that do not appear in any of the trees posted above.   In some cases, primarily with regard to SNPs reported by Family Tree DNA based upon the results of Big Y testing or Geno 2.0 testing, the reported SNPs are ancestral to the SNPs set forth in one or more of the trees above; if the tested man is Ashkenazi on his direct male line, Big Y testing would likely determine that he belongs to one of the clusters set forth above. In other instances, it is possible that SNPs identify a small and/or undertested Ashkenazi cluster; further testing or information may identify such clusters.  Often, because the methodology used herein to identify potential Ashkenazi SNPs is overinclusive (especially for the 50 cM cohort but also, on occasion, for the 80 cM and 100 cM cohorts), SNPs set forth below do not reflect Ashkenazi (or Jewish) ancestry on the direct male line.  Finally, there are some SNPs (identified with "N/A") that do not appear on FTDNA's Y-DNA haplotree at all.

Upstream SNPs.  The following SNPs in the table above (identified in red) are upstream from SNPs found in one or more Ashkenazi Y-DNA clusters: A2512, CTS10228, L596, L621, M170, M223, M423, P215, P37, P78, .  

If men who are reported based upon STR or Geno 2.0 testing as having these SNPs are of Ashkenazi descent on their direct male line, there is a high probability that such men belong to one of those Ashkenazi Y-DNA clusters.  However, a large proportion of the men reported as having these terminal SNPs are not of Ashkenazi descent on their direct male lines.

Downstream SNP that may reflect an Ashkenazi Y-DNA line.  A1965 (identified in blue) does not appear in the Ashkenazi Y-DNA trees posted above, but may reflect an Ashkenazi Y-DNA line.

Other SNPs.  With the exception of the SNPs that are not on FTDNA's Y-DNA Haplotree (identified with "N/A"), it is unlikely that men reported as having terminal SNPs other than the upstream SNPs identified above are of Ashkenazi descent on their direct male lines.